There is absolutely no reason to reinvent the wheel. Fortunately, there are computational scientists that are really good at creating useful wheels. A classic example is the widely used numerical linear algebra package called LAPACK. It is a collection of useful functions for handling numerical linear algebra problems. The package is large and has many more options than can be covered in this text, so just a few examples are included of calling representative functions that will be particularly useful for the projects in this book. Use the documentation for the libraries to take full advantage of their capabilities. In this chapter, we will see how to incorporate library content into programs both during the compile stage and in the link stage of building an executable. We will then explore the BLAS and LAPACK libraries for linear algebra operations, the FFTW library for doing fast Fourier transforms (FFTs), and also some basic concepts related to random number generation. These topics will all be of particular relevance to the computing projects proposed at the end of Part I.