diff --git a/collections-lists/ConcatenateLists/BenchmarkRunner/BenchmarkRunner.csproj b/collections-lists/ConcatenateLists/BenchmarkRunner/BenchmarkRunner.csproj
index 2ea5b608b0..bea7f628bb 100644
--- a/collections-lists/ConcatenateLists/BenchmarkRunner/BenchmarkRunner.csproj
+++ b/collections-lists/ConcatenateLists/BenchmarkRunner/BenchmarkRunner.csproj
@@ -2,13 +2,13 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
 	<ItemGroup>
-		<PackageReference Include="BenchmarkDotNet" Version="0.13.1" />
+		<PackageReference Include="BenchmarkDotNet" Version="0.15.8" />
 	</ItemGroup>
 
 	<ItemGroup>
diff --git a/collections-lists/ConcatenateLists/BenchmarkRunner/ConcatenatorBenchmark.cs b/collections-lists/ConcatenateLists/BenchmarkRunner/ConcatenatorBenchmark.cs
index 1d5a1552de..65f5bd41ba 100644
--- a/collections-lists/ConcatenateLists/BenchmarkRunner/ConcatenatorBenchmark.cs
+++ b/collections-lists/ConcatenateLists/BenchmarkRunner/ConcatenatorBenchmark.cs
@@ -9,14 +9,30 @@ namespace BenchmarkRunner
     [Orderer(SummaryOrderPolicy.FastestToSlowest)]
     public class ConcatenatorBenchmark
     {
-        private readonly List<string> _firstList = Enumerable.Repeat("Code", 1_000_000).ToList();
-        private readonly List<string> _secondList = Enumerable.Repeat("Maze", 1_000_000).ToList();
+        [Params(50_000, 1_000_000)]
+        public int Size;
+
+        private List<string> _firstList = [];
+        private List<string> _secondList = [];
         private readonly Concatenator _concatenator = new();
-               
+
+        [GlobalSetup]
+        public void Setup()
+        {
+            _firstList = Enumerable.Range(0, Size).Select(i => $"Code{i}").ToList();
+            _secondList = Enumerable.Range(0, Size).Select(i => $"Maze{i}").ToList();
+        }
+
         [Benchmark]
         public void UsingAdd()
         {
-             _concatenator.UsingAdd(_firstList, _secondList);
+            _concatenator.UsingAdd(_firstList, _secondList);
+        }
+
+        [Benchmark]
+        public void UsingAddNoCapacity()
+        {
+            _concatenator.UsingAddNoCapacity(_firstList, _secondList);
         }
 
         [Benchmark]
@@ -37,6 +53,12 @@ public void UsingAddRange()
             _concatenator.UsingAddRange(_firstList, _secondList);
         }
 
+        [Benchmark]
+        public void UsingAddRangeNoCapacity()
+        {
+            _concatenator.UsingAddRangeNoCapacity(_firstList, _secondList);
+        }
+
         [Benchmark]
         public void UsingCopyTo()
         {
@@ -48,5 +70,11 @@ public void UsingSelectMany()
         {
             _concatenator.UsingSelectMany(_firstList, _secondList);
         }
+
+        [Benchmark]
+        public void UsingCollectionExpression()
+        {
+            _concatenator.UsingCollectionExpression(_firstList, _secondList);
+        }
     }
 }
diff --git a/collections-lists/ConcatenateLists/ConcatenateLists/ConcatenateLists.csproj b/collections-lists/ConcatenateLists/ConcatenateLists/ConcatenateLists.csproj
index 74abf5c976..dfb40caafc 100644
--- a/collections-lists/ConcatenateLists/ConcatenateLists/ConcatenateLists.csproj
+++ b/collections-lists/ConcatenateLists/ConcatenateLists/ConcatenateLists.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/collections-lists/ConcatenateLists/ConcatenateLists/Concatenator.cs b/collections-lists/ConcatenateLists/ConcatenateLists/Concatenator.cs
index dd505c0412..56399d6f73 100644
--- a/collections-lists/ConcatenateLists/ConcatenateLists/Concatenator.cs
+++ b/collections-lists/ConcatenateLists/ConcatenateLists/Concatenator.cs
@@ -4,7 +4,24 @@ public class Concatenator
     {
         public List<string> UsingAdd(List<string> firstList, List<string> secondList)
         {
-            var result = new List<string>(firstList.Count() + secondList.Count());
+            var result = new List<string>(firstList.Count + secondList.Count);
+
+            foreach (var item in firstList)
+            {
+                result.Add(item);
+            }
+
+            foreach (var item in secondList)
+            {
+                result.Add(item);
+            }
+
+            return result;
+        }
+
+        public List<string> UsingAddNoCapacity(List<string> firstList, List<string> secondList)
+        {
+            var result = new List<string>();
 
             foreach (var item in firstList)
             {
@@ -31,7 +48,17 @@ public List<string> UsingEnumerableUnion(List<string> firstList, List<string> se
 
         public List<string> UsingAddRange(List<string> firstList, List<string> secondList)
         {
-            var result = new List<string>(firstList.Count() + secondList.Count());
+            var result = new List<string>(firstList.Count + secondList.Count);
+
+            result.AddRange(firstList);
+            result.AddRange(secondList);
+
+            return result;
+        }
+
+        public List<string> UsingAddRangeNoCapacity(List<string> firstList, List<string> secondList)
+        {
+            var result = new List<string>();
 
             result.AddRange(firstList);
             result.AddRange(secondList);
@@ -41,19 +68,26 @@ public List<string> UsingAddRange(List<string> firstList, List<string> secondLis
 
         public List<string> UsingCopyTo(List<string> firstList, List<string> secondList)
         {
-            var combinedList = new string[firstList.Count() + secondList.Count()];
+            var combinedArray = new string[firstList.Count + secondList.Count];
 
-            firstList.CopyTo(combinedList);
-            secondList.CopyTo(combinedList, firstList.Count());
+            firstList.CopyTo(combinedArray, 0);
+            secondList.CopyTo(combinedArray, firstList.Count);
 
-            return combinedList.ToList();
+            return combinedArray.ToList();
         }
 
         public List<string> UsingSelectMany(List<string> firstList, List<string> secondList)
-        {  
+        {
             var combinedArray = new[] { firstList, secondList }.SelectMany(x => x);
 
             return combinedArray.ToList();
         }
+
+        public List<string> UsingCollectionExpression(List<string> firstList, List<string> secondList)
+        {
+            List<string> result = [.. firstList, .. secondList];
+
+            return result;
+        }
     }
 }
diff --git a/collections-lists/ConcatenateLists/ConcatenateLists/Program.cs b/collections-lists/ConcatenateLists/ConcatenateLists/Program.cs
index 2cee91b4bd..903fc38b57 100644
--- a/collections-lists/ConcatenateLists/ConcatenateLists/Program.cs
+++ b/collections-lists/ConcatenateLists/ConcatenateLists/Program.cs
@@ -1,46 +1,42 @@
-namespace ConcatenateLists;
+using ConcatenateLists;
 
-public class Program
-{
-    public static void Main()
-    {
-        Console.WriteLine("---------- Concatenate Lists in C# ----------");
+Console.WriteLine("---------- Concatenate Lists in C# ----------");
 
-        var firstList = new List<string>() { "Code", "Maze", "Concatenate" };
-        var secondList = new List<string>() { "Lists", "in", "C#" };
+var firstList = new List<string>() { "Code", "Maze", "Concatenate" };
+var secondList = new List<string>() { "Lists", "in", "C#" };
 
-        var concatenator = new Concatenator();
+var concatenator = new Concatenator();
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate lists using Add");
-        PrintOut(concatenator.UsingAdd(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate lists using Add");
+PrintOut(concatenator.UsingAdd(firstList, secondList));
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate using Enumerable.Concat");
-        PrintOut(concatenator.UsingEnumerableConcat(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using Enumerable.Concat");
+PrintOut(concatenator.UsingEnumerableConcat(firstList, secondList));
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate using Enumerable.Union");
-        PrintOut(concatenator.UsingEnumerableUnion(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using Enumerable.Union");
+PrintOut(concatenator.UsingEnumerableUnion(firstList, secondList));
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate using AddRange");
-        PrintOut(concatenator.UsingAddRange(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using AddRange");
+PrintOut(concatenator.UsingAddRange(firstList, secondList));
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate using List CopyTo");
-        PrintOut(concatenator.UsingCopyTo(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using List CopyTo");
+PrintOut(concatenator.UsingCopyTo(firstList, secondList));
 
-        Console.WriteLine();
-        Console.WriteLine("------ Concatenate using SelectMany");
-        PrintOut(concatenator.UsingSelectMany(firstList, secondList));
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using SelectMany");
+PrintOut(concatenator.UsingSelectMany(firstList, secondList));
 
-        Console.ReadLine();
-    }
+Console.WriteLine();
+Console.WriteLine("------ Concatenate using a collection expression");
+PrintOut(concatenator.UsingCollectionExpression(firstList, secondList));
 
-    private static void PrintOut(List<string> list)
-    {
-        list.ForEach(x => Console.Write($" => {x}"));
-        Console.WriteLine();
-    }
+static void PrintOut(List<string> list)
+{
+    list.ForEach(x => Console.Write($" => {x}"));
+    Console.WriteLine();
 }
diff --git a/collections-lists/ConcatenateLists/Tests/Tests.cs b/collections-lists/ConcatenateLists/Tests/Tests.cs
index 1e4282e3a0..2a0c7447a5 100644
--- a/collections-lists/ConcatenateLists/Tests/Tests.cs
+++ b/collections-lists/ConcatenateLists/Tests/Tests.cs
@@ -15,7 +15,16 @@ public void GivenTwoLists_WhenUsingAddMethod_ThenReturnANewConcatenatedList()
         {
             var result = _concatenator.UsingAdd(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
+            Assert.Equal(_expectedList, result);
+        }
+
+        [Fact]
+        public void GivenTwoLists_WhenUsingAddNoCapacityMethod_ThenReturnANewConcatenatedList()
+        {
+            var result = _concatenator.UsingAddNoCapacity(_firstList, _secondList);
+
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
 
@@ -24,7 +33,7 @@ public void GivenTwoLists_WhenUsingEnumerableConcatMethod_ThenReturnANewConcaten
         {
             var result = _concatenator.UsingEnumerableConcat(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
 
@@ -33,7 +42,7 @@ public void GivenTwoLists_WhenUsingEnumerableUnionMethod_ThenReturnANewConcatena
         {
             var result = _concatenator.UsingEnumerableUnion(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
 
@@ -42,7 +51,16 @@ public void GivenTwoLists_WhenUsingAddRangeMethod_ThenReturnANewConcatenatedList
         {
             var result = _concatenator.UsingAddRange(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
+            Assert.Equal(_expectedList, result);
+        }
+
+        [Fact]
+        public void GivenTwoLists_WhenUsingAddRangeNoCapacityMethod_ThenReturnANewConcatenatedList()
+        {
+            var result = _concatenator.UsingAddRangeNoCapacity(_firstList, _secondList);
+
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
 
@@ -51,7 +69,7 @@ public void GivenTwoLists_WhenUsingCopyToMethod_ThenReturnANewConcatenatedList()
         {
             var result = _concatenator.UsingCopyTo(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
 
@@ -60,8 +78,25 @@ public void GivenTwoLists_WhenUsingSelectManyMethod_ThenReturnANewConcatenatedLi
         {
             var result = _concatenator.UsingSelectMany(_firstList, _secondList);
 
-            Assert.Equal(_expectedList.Count(), result.Count);
+            Assert.Equal(_expectedList.Count, result.Count);
             Assert.Equal(_expectedList, result);
         }
+
+        [Fact]
+        public void GivenTwoLists_WhenUsingCollectionExpression_ThenReturnANewConcatenatedList()
+        {
+            var result = _concatenator.UsingCollectionExpression(_firstList, _secondList);
+
+            Assert.Equal(_expectedList.Count, result.Count);
+            Assert.Equal(_expectedList, result);
+        }
+
+        [Fact]
+        public void GivenListsWithDuplicates_WhenUsingEnumerableUnionMethod_ThenReturnEachValueOnce()
+        {
+            var result = _concatenator.UsingEnumerableUnion(new List<string> { "a", "a" }, new List<string> { "a" });
+
+            Assert.Equal(new List<string> { "a" }, result);
+        }
     }
-}
\ No newline at end of file
+}
diff --git a/collections-lists/ConcatenateLists/Tests/Tests.csproj b/collections-lists/ConcatenateLists/Tests/Tests.csproj
index 8e094886bb..6d8aa37c6f 100644
--- a/collections-lists/ConcatenateLists/Tests/Tests.csproj
+++ b/collections-lists/ConcatenateLists/Tests/Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net6.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -9,13 +9,13 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
-    <PackageReference Include="xunit" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.10.1" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="coverlet.collector" Version="3.1.2">
+    <PackageReference Include="coverlet.collector" Version="10.1.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>