variable 1 onto stack add // pop and add the top two stack items then push the result onto the stack stloc.0 // pop and store the top stack item to local variable 0 In the latter example, the values of the two registers, eax and edx, are first pushed on the stack. When the add-instruction is called the operands are "popped", or retrieved, and the result is "pushed", or stored, on the stack. The resulting value is then popped from the stack and stored in eax. Object-oriented concepts CIL is designed to be object-oriented. You may create objects, call methods, and use other types of members, such as fields. Every method needs (with some exceptions) to reside in a class. So does this static method: .class public Foo { .method public static int32 Add(int32, int32) cil managed { .maxstack 2 ldarg.0 // load the first argument; ldarg.1 // load the second argument; add // add them; ret // return the result; } } The method Add does not require any instance of Foo to be declared because it is declared as static, and it may then be used like this in C#: int r = Foo.Add(2, 3); // 5 In CIL it would look like this: ldc.i4.2 ldc.i4.3 call int32 Foo::Add(int32, int32) stloc.0 Instance classes An instance class contains at least one constructor and some instance members. The following class has a set of methods representing actions of a Car-object. .class public Car { .method public specialname rtspecialname instance void .ctor(int32, int32) cil managed { /* Constructor */ } .method public void Move(int32) cil managed { /* Omitting implementation */ } .method public void TurnRight() cil managed { /* Omitting implementation */ } .method public void TurnLeft() cil managed { /* Omitting implementation */ } .method public void Brake() cil managed { /* Omitting implementation */ } } Creating objects In C# class instances are created like this: Car myCar = new Car(1, 4); Car yourCar = new Car(1, 3); And those statements are roughly the same as these instructions in CIL: ldc.i4.1 ldc.i4.4 newobj instance void Car::.ctor(int, int) stloc.0 // myCar = new Car(1, 4); ldc.i4.1 ldc.i4.3 newobj instance void Car::.ctor(int, int) stloc.1 // yourCar = new Car(1, 3); Invoking instance methods Instance methods are invoked in C# as the one that follows: myCar.Move(3); As invoked in CIL: ldloc.0 // Load the object "myCar" on the stack ldc.i4.3