This article describes the importance of selecting the appropriate epidemiological study design for a given study question. It provides an explanation to the different terms used in describing study designs with regards to observational versus interventional and descriptive versus analytical types of study designs. This article focuses on the description of the different types of descriptive study designs, that is, case report, case series, correlational, and cross-sectional study designs. The requirements for selecting these study designs are discussed along with the advantages and disadvantages of each study design. The descriptive studies are similar in the context that they are based on a single sample with no comparative group within the study design. Their basic purpose is to describe the characteristics of the sample with regards to the characteristics that are present and so are useful in generating a hypothesis. The absence of a comparative group is the main limitation of the descriptive studies, and this is the reason they cannot be used to determine an association by testing a hypothesis showing a relationship between a risk factor and disease. The analytical study designs will be discussed in the next article in this series