Welcome to the second course in the Epidemiology for Public Health specialization. I'm Dr. Filippos Filippidis, and in this course, with the help of my experienced colleagues at Imperial College London, we will introduce you to the main study designs in epidemiological research. We build on concepts described in the first course. So, please check it out if you haven't already. Many of you may already know some of the study designs, either from your studies, or simply by reading the news. What we aim to do with this course, is to systematically describe the various methodological approaches in epidemiological research, and highlight the strengths and weaknesses through real-life examples. Not all study designs are born equal. It is widely accepted that results from certain types of studies, are more likely to reflect the truth than others. This is often called Hierarchy of Evidence and considers systematic reviews, meta-analysis, and randomized controlled trials, as the best sources of evidence. While this is mostly true, it does not account for the quality of studies. Many would argue that a well conducted case-control study, can be more informative than a trial with methodological problems. Feasibility, time, and ethical considerations are also important. For instance, there are certain set of questions, which cannot be explored through randomized trials for ethical and practical reasons. Throughout this course, we will discuss each of the study design separately, and identify when each one is most relevant. You will also explore methodological details, that will help you reflect on the strength of evidence generated by epidemiological studies. To do so, I encourage you to not only watch the videos, but engage with the questions and the readings in the course. By the time you have completed all four weeks of the course, you will be able to critically discuss all the main types of original epidemiological research, and you will be in good stead to start designing your own studies. Join us in our exciting journey, as we explore how we can investigate into a research question, trying to find the optimal way to generate and analyze data on each occasion.