Recombinant production of proteins is one of the most powerful techniques used in the Life Sciences. The ability to produce and purify an abundance of a desired recombinant protein can permit a wide range of possibilities including, its use in industrial processes, or its use to diagnose or treat disease. At first glance, recombinant protein expression looks quite simple. Essentially, DNA encoding a target protein is cloned downstream of a promoter in an expression vector. This vector is then introduced into a host cell, and the cell’s protein synthesis machinery produces the desired protein. In practice, however, protein expression can be very challenging because so many factors may influence the process. For example, each protein folds in its own unique manner, a process that may be influenced by the choice of expression host. Similarly, some proteins require post-translational modifications or proper insertion into a biological membrane. Finally, some proteins may have an activity that is detrimental to the host. Thus, no single solution exists for successful production of all recombinant proteins. Instead, it is beneficial to have access to a wide range of expression tools, and a willingness to explore multiple approaches to better one’s chances for success.