diff --git a/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.cs b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.cs
new file mode 100644
index 00000000000..fe5617c228a
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.cs
@@ -0,0 +1,78 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+
+class MissedCastOpportunity
+{
+    public void M1(List<Animal> animals)
+    {
+        // BAD: Can be replaced with animals.Cast<Dog>().
+        foreach (Animal a in animals)
+        {
+            Dog d = (Dog)a;
+            d.Woof();
+        }
+    }
+
+    public void M2(NonEnumerableClass nec)
+    {
+        // GOOD: Not possible to use Linq here.
+        foreach (Animal a in nec)
+        {
+            Dog d = (Dog)a;
+            d.Woof();
+        }
+    }
+
+    public void M3(Animal[] animals)
+    {
+        // BAD: Can be replaced with animals.Cast<Dog>().
+        foreach (Animal animal in animals)
+        {
+            Dog d = (Dog)animal;
+            d.Woof();
+        }
+    }
+
+    public void M4(Array animals)
+    {
+        // BAD: Can be replaced with animals.Cast<Dog>().
+        foreach (Animal animal in animals)
+        {
+            Dog d = (Dog)animal;
+            d.Woof();
+        }
+    }
+
+    public void M5(IEnumerable animals)
+    {
+        // BAD: Can be replaced with animals.Cast<Dog>().
+        foreach (object animal in animals)
+        {
+            Dog d = (Dog)animal;
+            d.Woof();
+        }
+    }
+
+    public class NonEnumerableClass
+    {
+        public IEnumerator<Animal> GetEnumerator() => throw null;
+    }
+
+    public class Animal { }
+
+    class Dog : Animal
+    {
+        private string name;
+
+        public Dog(string name)
+        {
+            this.name = name;
+        }
+
+        public void Woof()
+        {
+            Console.WriteLine("Woof! My name is " + name + ".");
+        }
+    }
+}
\ No newline at end of file
diff --git a/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.expected b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.expected
new file mode 100644
index 00000000000..7e08d734acc
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.expected
@@ -0,0 +1,4 @@
+| MissedCastOpportunity.cs:10:9:14:9 | foreach (... ... in ...) ... | This foreach loop immediately $@ - consider casting the sequence explicitly using '.Cast(...)'. | MissedCastOpportunity.cs:12:13:12:27 | ... ...; | casts its iteration variable to another type |
+| MissedCastOpportunity.cs:30:9:34:9 | foreach (... ... in ...) ... | This foreach loop immediately $@ - consider casting the sequence explicitly using '.Cast(...)'. | MissedCastOpportunity.cs:32:13:32:32 | ... ...; | casts its iteration variable to another type |
+| MissedCastOpportunity.cs:40:9:44:9 | foreach (... ... in ...) ... | This foreach loop immediately $@ - consider casting the sequence explicitly using '.Cast(...)'. | MissedCastOpportunity.cs:42:13:42:32 | ... ...; | casts its iteration variable to another type |
+| MissedCastOpportunity.cs:50:9:54:9 | foreach (... ... in ...) ... | This foreach loop immediately $@ - consider casting the sequence explicitly using '.Cast(...)'. | MissedCastOpportunity.cs:52:13:52:32 | ... ...; | casts its iteration variable to another type |
diff --git a/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.qlref b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.qlref
new file mode 100644
index 00000000000..8d70f999503
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/MissedCastOpportunity.qlref
@@ -0,0 +1 @@
+Linq/MissedCastOpportunity.ql
diff --git a/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/options b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/options
new file mode 100644
index 00000000000..75c39b4541b
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedCastOpportunity/options
@@ -0,0 +1,2 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj
diff --git a/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.cs b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.cs
new file mode 100644
index 00000000000..d1326c70ee2
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.cs
@@ -0,0 +1,83 @@
+using System;
+using System.Linq;
+using System.Collections.Generic;
+
+class MissedWhereOpportunity
+{
+    public void M1(List<int> lst)
+    {
+        // BAD: Can be replaced with lst.Where(e => e % 2 == 0)
+        foreach (int i in lst)
+        {
+            if (i % 2 != 0)
+                continue;
+            Console.WriteLine(i);
+            Console.WriteLine((i / 2));
+        }
+
+        // BAD: Can be replaced with lst.Where(e => e % 2 == 0)
+        foreach (int i in lst)
+        {
+            if (i % 2 == 0)
+            {
+                Console.WriteLine(i);
+                Console.WriteLine((i / 2));
+            }
+        }
+    }
+
+    public void M2(NonEnumerableClass nec)
+    {
+        // GOOD: Linq can't be used here.
+        foreach (int i in nec)
+        {
+            if (i % 2 == 0)
+            {
+                Console.WriteLine(i);
+                Console.WriteLine((i / 2));
+            }
+        }
+    }
+
+    public void M3(int[] arr)
+    {
+        // BAD: Can be replaced with arr.Where(e => e % 2 == 0)
+        foreach (var n in arr)
+        {
+            if (n % 2 == 0)
+            {
+                Console.WriteLine(n);
+                Console.WriteLine((n / 2));
+            }
+        }
+    }
+
+    public void M4(Array arr)
+    {
+        // GOOD: Linq can't be used here.
+        foreach (var element in arr)
+        {
+            if (element.GetHashCode() % 2 == 0)
+            {
+                Console.WriteLine(element);
+            }
+        }
+    }
+
+    public void M5(IEnumerable<int> elements)
+    {
+        // BAD: Can be replaced with elements.Where(e => e.GetHashCode() % 2 == 0)
+        foreach (var element in elements)
+        {
+            if (element.GetHashCode() % 2 == 0)
+            {
+                Console.WriteLine(element);
+            }
+        }
+    }
+
+    public class NonEnumerableClass
+    {
+        public IEnumerator<int> GetEnumerator() => throw null;
+    }
+}
diff --git a/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.expected b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.expected
new file mode 100644
index 00000000000..5efde9aebed
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.expected
@@ -0,0 +1,4 @@
+| MissedWhereOpportunity.cs:10:9:16:9 | foreach (... ... in ...) ... | This foreach loop $@ - consider filtering the sequence explicitly using '.Where(...)'. | MissedWhereOpportunity.cs:12:17:12:26 | ... != ... | implicitly filters its target sequence |
+| MissedWhereOpportunity.cs:19:9:26:9 | foreach (... ... in ...) ... | This foreach loop $@ - consider filtering the sequence explicitly using '.Where(...)'. | MissedWhereOpportunity.cs:21:17:21:26 | ... == ... | implicitly filters its target sequence |
+| MissedWhereOpportunity.cs:45:9:52:9 | foreach (... ... in ...) ... | This foreach loop $@ - consider filtering the sequence explicitly using '.Where(...)'. | MissedWhereOpportunity.cs:47:17:47:26 | ... == ... | implicitly filters its target sequence |
+| MissedWhereOpportunity.cs:70:9:76:9 | foreach (... ... in ...) ... | This foreach loop $@ - consider filtering the sequence explicitly using '.Where(...)'. | MissedWhereOpportunity.cs:72:17:72:46 | ... == ... | implicitly filters its target sequence |
diff --git a/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.qlref b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.qlref
new file mode 100644
index 00000000000..4a08b459a6c
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/MissedWhereOpportunity.qlref
@@ -0,0 +1 @@
+Linq/MissedWhereOpportunity.ql
diff --git a/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/options b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/options
new file mode 100644
index 00000000000..75c39b4541b
--- /dev/null
+++ b/csharp/ql/test/query-tests/Linq/MissedWhereOpportunity/options
@@ -0,0 +1,2 @@
+semmle-extractor-options: /nostdlib /noconfig
+semmle-extractor-options: --load-sources-from-project:${testdir}/../../../resources/stubs/_frameworks/Microsoft.NETCore.App/Microsoft.NETCore.App.csproj