There has been an increasing number of randomized clinical trials conducted and published which provide the cornerstone of evidence-based medicine. More and more people from a broad range of professional backgrounds need to understand the essentials of clinical trials regarding their design, statistical analysis, and reporting. In this chapter, we provided an introduction to the area of clinical trials covering some of the key issues to be considered in their design, analysis and interpretation. Firstly, we described the general aims of clinical trials and their classifications according to different criteria. Secondly, we introduced some essential design issues in clinical trials, including endpoints, patient selection, protocol development, randomization, blinding, and sample size determination. Thirdly, we discussed three possible sources of errors that may influence trial results: bias/systematic errors, confounding, and random error. Next, we described some basic statistical concepts and methods frequently used in the analysis of randomized trials. These included descriptive statistics, statistical inferences, techniques for the comparison of means or proportions from two samples, and survival analysis. To facilitate understanding of the concepts, we also provided frequently used statistical terms and their meanings. In conclusion, readers should have sufficient knowledge, via the concepts discussed in this chapter, to appreciate the essential elements of most clinical trial reports.