The authors would like to thank Alex Nones for proofreading the manuscript during its various stages. Also, thanks to Karl Broman for contributing the “Plots to Avoid” section and to Stephanie Hicks for designing some of the exercises. This book was conceived during the teaching of several HarvardX courses, coordinated by Heather Sternshein. We are also grateful to all the students whose questions and comments helped us improve the book. The courses were partially funded by NIH grant R25GM114818. We are very grateful to the Nati onal Institute of Health for its support. A special thanks goes to all those that edited the book via GitHub pull requests: vjcitn, yeredh, stefan, molx, kern3020, josemrecio, hcorrada, neerajt, massie, jmgore75, molecules, lzamparo, eronisko, and obicke. Cover image credit: this photograph is La Mina Falls, El Yunque National Forest, Puerto Rico, taken by Ron Kroetz https://www.flickr.com/photos/ronkroetz/14779273923 Attribution-NoDerivs 2.0 Generic (CC BY-ND 2.0) onal Institute of Health for its support. A special thanks goes to all those that edited the book via GitHub pull requests: vjcitn, yeredh, stefan, molx, kern3020, josemrecio, hcorrada, neerajt, massie, jmgore75, molecules, lzamparo, eronisko, and obicke. Cover image credit: this photograph is La Mina Falls, El Yunque National Forest, Puerto Rico, taken by Ron Kroetz https://www.flickr.com/photos/ronkroetz/14779273923 Attribution-NoDerivs 2.0 Generic (CC BY-ND 2.0)