In this section we will move from the formally exact equations of CC theory as presented in the previous section, to the practical issues concerning computer implementation. This requires, first of all, some effort in the construction of the CC equations themselves. We will approach this task from two perspectives: (1) algebraic manipulation of strings of annihilation and creation operators, and (2) diagrammatic analyses. Both of these techniques give special insights into the structure of the final equations, and we will deal with them explicitly. For both methods, the concept of a normal-ordered operator and Wick's theorem will be important.