diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionModel.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionModel.cs
index b1bf4906..a4da969e 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionModel.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionModel.cs
@@ -88,6 +88,7 @@ public SolutionModel(SolutionModel solutionModel)
         }
 
         this.Description = solutionModel.Description;
+        this.SortOrder = solutionModel.SortOrder;
         this.solutionBuildTypes = [.. solutionModel.solutionBuildTypes];
         this.solutionPlatforms = [.. solutionModel.solutionPlatforms];
         this.projectTypes = [.. solutionModel.projectTypes];
@@ -111,6 +112,15 @@ public SolutionModel(SolutionModel solutionModel)
     /// </summary>
     public string? Description { get; set; }
 
+    /// <summary>
+    /// Gets or sets the order in which solution items are written to a .slnx file.
+    /// </summary>
+    /// <remarks>
+    /// The default is <see cref="SolutionSortOrder.Alphabetical"/>, which groups items by type and sorts them alphabetically.
+    /// Set to <see cref="SolutionSortOrder.Document"/> to preserve the order the items appear in the solution file.
+    /// </remarks>
+    public SolutionSortOrder SortOrder { get; set; }
+
     /// <summary>
     /// Gets the list of solution items in the solution.
     /// This is all of the solution folders and projects in the solution.
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionSortOrder.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionSortOrder.cs
new file mode 100644
index 00000000..76dfecdb
--- /dev/null
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionSortOrder.cs
@@ -0,0 +1,20 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Microsoft.VisualStudio.SolutionPersistence.Model;
+
+/// <summary>
+/// Specifies how solution items are ordered when serializing a .slnx file.
+/// </summary>
+public enum SolutionSortOrder
+{
+    /// <summary>
+    /// Items are grouped by type and sorted alphabetically. This is the default.
+    /// </summary>
+    Alphabetical = 0,
+
+    /// <summary>
+    /// Items are written in document order, i.e. the order the elements appear in the solution file.
+    /// </summary>
+    Document = 1,
+}
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/PublicAPI/PublicAPI.Unshipped.txt b/src/Microsoft.VisualStudio.SolutionPersistence/PublicAPI/PublicAPI.Unshipped.txt
index d34f9569..2c0f9ea8 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/PublicAPI/PublicAPI.Unshipped.txt
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/PublicAPI/PublicAPI.Unshipped.txt
@@ -34,4 +34,9 @@ Microsoft.VisualStudio.SolutionPersistence.Model.SolutionErrorType.UnsupportedVe
 Microsoft.VisualStudio.SolutionPersistence.Model.SolutionException.ErrorType.get -> Microsoft.VisualStudio.SolutionPersistence.Model.SolutionErrorType?
 Microsoft.VisualStudio.SolutionPersistence.Model.SolutionException.ErrorType.init -> void
 Microsoft.VisualStudio.SolutionPersistence.Model.SolutionException.SolutionException(string! message, Microsoft.VisualStudio.SolutionPersistence.Model.SolutionErrorType errorType) -> void
-Microsoft.VisualStudio.SolutionPersistence.Model.SolutionException.SolutionException(string! message, System.Exception! inner, Microsoft.VisualStudio.SolutionPersistence.Model.SolutionErrorType errorType) -> void
\ No newline at end of file
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionException.SolutionException(string! message, System.Exception! inner, Microsoft.VisualStudio.SolutionPersistence.Model.SolutionErrorType errorType) -> void
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionModel.SortOrder.get -> Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionModel.SortOrder.set -> void
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder.Alphabetical = 0 -> Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder
+Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder.Document = 1 -> Microsoft.VisualStudio.SolutionPersistence.Model.SolutionSortOrder
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Keywords.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Keywords.cs
index 63c95801..f65cd107 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Keywords.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Keywords.cs
@@ -16,6 +16,7 @@ internal enum Keyword
     // Solution properties
     Description,
     Version,
+    Sort,
 
     // Solution sections
     Configurations,
@@ -64,6 +65,8 @@ internal static class Keywords
     internal const string XmlTrue = "true";
     internal const string XmlFalse = "false";
 
+    internal const string SortDocument = "Document";
+
     private static readonly string[] KeywordToString;
     private static readonly Lictionary<string, Keyword> StringToKeyword;
 
@@ -74,6 +77,7 @@ static Keywords()
                 new(nameof(Keyword.Solution), Keyword.Solution),
                 new(nameof(Keyword.Description), Keyword.Description),
                 new(nameof(Keyword.Version), Keyword.Version),
+                new(nameof(Keyword.Sort), Keyword.Sort),
                 new(nameof(Keyword.Configurations), Keyword.Configurations),
                 new(nameof(Keyword.Folder), Keyword.Folder),
                 new(nameof(Keyword.Project), Keyword.Project),
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Slnx.xsd b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Slnx.xsd
index 399bf6ed..e6caf5f2 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Slnx.xsd
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/Slnx.xsd
@@ -9,6 +9,7 @@
             </xs:choice>
             <xs:attribute name="Description" type="xs:string" />
             <xs:attribute name="Version" type="xs:string" />
+            <xs:attribute name="Sort" type="xs:string" />
         </xs:complexType>
     </xs:element>
 
@@ -115,4 +116,4 @@
             </xs:element>
         </xs:choice>
     </xs:group>
-</xs:schema>
\ No newline at end of file
+</xs:schema>
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/ItemRefList`1.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/ItemRefList`1.cs
index 36c75fea..a9456bf3 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/ItemRefList`1.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/ItemRefList`1.cs
@@ -48,6 +48,8 @@ internal readonly void Add(T item)
 
     internal readonly T? FirstOrDefault() => this.items.Count > 0 ? this.items[0] : null;
 
+    internal readonly bool TryGet(string itemRef, [NotNullWhen(true)] out T? item) => this.items.TryGetValue(itemRef, out item);
+
     // Finds the item that would be immediately after the given item ref.
     internal readonly bool TryFindNext(string itemRef, out T? item)
     {
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlContainer.ApplyModel.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlContainer.ApplyModel.cs
index d5543ae2..fb76f793 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlContainer.ApplyModel.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlContainer.ApplyModel.cs
@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Xml;
+using Microsoft.VisualStudio.SolutionPersistence.Model;
 using Microsoft.VisualStudio.SolutionPersistence.Utilities;
 
 namespace Microsoft.VisualStudio.SolutionPersistence.Serializer.Xml.XmlDecorators;
@@ -121,11 +122,19 @@ internal bool ApplyModelItemsToXml<TModelItem, TDecorator>(
         }
 
         // Add new elements that aren't already in the XML.
-        modelItems.Sort(decoratorItems.IgnoreCase ? ComparisonOrdinalIgnoreCase : ComparisonOrdinal);
+        bool documentOrder = this.Root.Solution?.SortOrder == SolutionSortOrder.Document;
+        if (!documentOrder)
+        {
+            modelItems.Sort(decoratorItems.IgnoreCase ? ComparisonOrdinalIgnoreCase : ComparisonOrdinal);
+        }
+
         foreach ((string itemRef, TModelItem modelItem) in modelItems)
         {
             // Find position to insert before based on general areas and alphabetical order.
-            XmlDecorator? insertBefore = decoratorItems.TryFindNext(itemRef, out TDecorator? insertBeforeLocal) ? insertBeforeLocal : this.FindNextDecorator<TDecorator>();
+            // In document order mode new items are appended to the end of their area in model order.
+            XmlDecorator? insertBefore = documentOrder
+                ? this.FindNextDecorator<TDecorator>()
+                : (decoratorItems.TryFindNext(itemRef, out TDecorator? insertBeforeLocal) ? insertBeforeLocal : this.FindNextDecorator<TDecorator>());
 
             TDecorator newDecorator = (TDecorator)this.CreateAndAddChild(decoratorElementName, itemRef, insertBefore);
             _ = applyModelToXml?.Invoke(newDecorator, modelItem);
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlFolder.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlFolder.cs
index dd75d2d1..cbcd4941 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlFolder.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlFolder.cs
@@ -94,9 +94,24 @@ internal void AddToModel(SolutionModel solutionModel, List<(XmlProject XmlProjec
                 properties.AddToModel(folderModel);
             }
 
-            foreach (XmlProject project in this.folderProjects.GetItems())
+            if (this.xmlSolution.SortOrder == SolutionSortOrder.Document)
             {
-                newProjects.Add((project, project.AddToModel(solutionModel)));
+                // Preserve the order the elements appear in the document.
+                foreach (XmlElement childElement in this.XmlElement.ChildElements())
+                {
+                    if (Keywords.ToKeyword(childElement.Name) == Keyword.Project &&
+                        this.folderProjects.TryGet(childElement.GetAttribute(Keyword.Path.ToXmlString()).Trim(), out XmlProject? project))
+                    {
+                        newProjects.Add((project, project.AddToModel(solutionModel)));
+                    }
+                }
+            }
+            else
+            {
+                foreach (XmlProject project in this.folderProjects.GetItems())
+                {
+                    newProjects.Add((project, project.AddToModel(solutionModel)));
+                }
             }
         }
         catch (Exception ex) when (SolutionException.ShouldWrap(ex))
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.ApplyModel.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.ApplyModel.cs
index 09b857e2..6046958f 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.ApplyModel.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.ApplyModel.cs
@@ -24,6 +24,12 @@ internal bool ApplyModelToXml(SolutionModel modelSolution)
             modified = true;
         }
 
+        if (this.SortOrder != modelSolution.SortOrder)
+        {
+            this.SortOrder = modelSolution.SortOrder;
+            modified = true;
+        }
+
         // Configurations
         // Use the item ref logic to allow only a single "Configurations" element, and use string.Empty as the item ref.
         modified |= this.ApplyModelItemsToXml<SolutionModel, XmlConfigurations>(
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.cs
index cb998ddc..e7c22e59 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/XmlDecorators/XmlSolution.cs
@@ -28,6 +28,18 @@ internal string? Version
         set => this.UpdateXmlAttribute(Keyword.Version, value);
     }
 
+    internal string? Sort
+    {
+        get => this.GetXmlAttribute(Keyword.Sort);
+        set => this.UpdateXmlAttribute(Keyword.Sort, value);
+    }
+
+    internal SolutionSortOrder SortOrder
+    {
+        get => StringComparer.OrdinalIgnoreCase.Equals(this.Sort, Keywords.SortDocument) ? SolutionSortOrder.Document : SolutionSortOrder.Alphabetical;
+        set => this.Sort = value == SolutionSortOrder.Document ? Keywords.SortDocument : null;
+    }
+
 #if DEBUG
 
     internal override string DebugDisplay => $"{base.DebugDisplay} RootProjects={this.rootProjects} Folders={this.folders}";
@@ -109,20 +121,48 @@ internal SolutionModel ToModel()
         {
             StringTable = this.Root.StringTable,
             Description = this.Description,
+            SortOrder = this.SortOrder,
 
             // Project types are loaded earlier when parsing the XML since they are needed to resolve projects.
             ProjectTypes = this.Root.ProjectTypes.ProjectTypes,
         };
 
         List<(XmlProject, SolutionProjectModel)> newProjects = new List<(XmlProject, SolutionProjectModel)>(this.rootProjects.ItemsCount);
-        foreach (XmlProject project in this.rootProjects.GetItems())
+        if (this.SortOrder == SolutionSortOrder.Document)
         {
-            newProjects.Add((project, project.AddToModel(solutionModel)));
+            // Preserve the order the elements appear in the document.
+            foreach (XmlElement childElement in this.XmlElement.ChildElements())
+            {
+                switch (Keywords.ToKeyword(childElement.Name))
+                {
+                    case Keyword.Project:
+                        if (this.rootProjects.TryGet(childElement.GetAttribute(Keyword.Path.ToXmlString()).Trim(), out XmlProject? project))
+                        {
+                            newProjects.Add((project, project.AddToModel(solutionModel)));
+                        }
+
+                        break;
+                    case Keyword.Folder:
+                        if (this.folders.TryGet(childElement.GetAttribute(Keyword.Name.ToXmlString()).Trim(), out XmlFolder? folder))
+                        {
+                            folder.AddToModel(solutionModel, newProjects);
+                        }
+
+                        break;
+                }
+            }
         }
-
-        foreach (XmlFolder folder in this.folders.GetItems())
+        else
         {
-            folder.AddToModel(solutionModel, newProjects);
+            foreach (XmlProject project in this.rootProjects.GetItems())
+            {
+                newProjects.Add((project, project.AddToModel(solutionModel)));
+            }
+
+            foreach (XmlFolder folder in this.folders.GetItems())
+            {
+                folder.AddToModel(solutionModel, newProjects);
+            }
         }
 
         // Dependencies need to be added after all the projects are loaded.
diff --git a/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/SortOrder.cs b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/SortOrder.cs
new file mode 100644
index 00000000..fbd3a1f1
--- /dev/null
+++ b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/SortOrder.cs
@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Serialization;
+
+/// <summary>
+/// Tests related to <see cref="SolutionSortOrder"/>.
+/// </summary>
+public class SortOrder
+{
+    /// <summary>
+    /// Ensures <see cref="SolutionSortOrder.Document"/> is written to the file and round-trips.
+    /// </summary>
+    [Fact]
+    public async Task DocumentRoundTripsAsync()
+    {
+        SolutionModel solution = new SolutionModel { SortOrder = SolutionSortOrder.Document };
+        _ = solution.AddProject("A.csproj");
+
+        (SolutionModel reserializedSolution, FileContents contents) = await SaveAndReopenModelAsync(SolutionSerializers.SlnXml, solution);
+
+        Assert.Contains("Sort=\"Document\"", contents.FullString);
+        Assert.Equal(SolutionSortOrder.Document, reserializedSolution.SortOrder);
+    }
+
+    /// <summary>
+    /// Ensures <see cref="SolutionSortOrder.Alphabetical"/> is omitted from the file and round-trips.
+    /// </summary>
+    [Fact]
+    public async Task AlphabeticalIsOmittedAsync()
+    {
+        SolutionModel solution = new SolutionModel();
+        _ = solution.AddProject("A.csproj");
+
+        (SolutionModel reserializedSolution, FileContents contents) = await SaveAndReopenModelAsync(SolutionSerializers.SlnXml, solution);
+
+        Assert.DoesNotContain("Sort=", contents.FullString);
+        Assert.Equal(SolutionSortOrder.Alphabetical, reserializedSolution.SortOrder);
+    }
+
+    /// <summary>
+    /// Ensures an unrecognized Sort value is treated as <see cref="SolutionSortOrder.Alphabetical"/>.
+    /// </summary>
+    [Fact]
+    public async Task UnknownSortValueIsAlphabeticalAsync()
+    {
+        const string slnx = """
+<Solution Sort="Bogus">
+  <Project Path="A.csproj" />
+</Solution>
+""";
+
+        using MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(slnx));
+        SolutionModel solution = await SolutionSerializers.SlnXml.OpenAsync(stream, CancellationToken.None);
+
+        Assert.Equal(SolutionSortOrder.Alphabetical, solution.SortOrder);
+    }
+
+    /// <summary>
+    /// Ensures the Sort value is parsed case-insensitively.
+    /// </summary>
+    [Fact]
+    public async Task SortValueIsCaseInsensitiveAsync()
+    {
+        const string slnx = """
+<Solution Sort="document">
+  <Project Path="A.csproj" />
+</Solution>
+""";
+
+        using MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(slnx));
+        SolutionModel solution = await SolutionSerializers.SlnXml.OpenAsync(stream, CancellationToken.None);
+
+        Assert.Equal(SolutionSortOrder.Document, solution.SortOrder);
+    }
+}