This chapter aims to arm clinical researchers with the necessary conceptual and practical tools (1) to understand what sample size or power analysis is, (2) to conduct such analyses for basic low-risk studies, and (3) to recognize when it is necessary to seek expert advice and input. I hope it is obvious that this chapter aims to serve as a general guide to the issues; specific details and mathematical presentations may be found in the cited literature. Additionally, it should be obvious that this discussion of statistical power is focused, appropriately, on quantitative investigations into real or hypothetical effects of treatments or interventions. It does not address qualitative study designs. The ultimate goal here is to help practicing clinical researcher get started with power analyses.