Should I open a Facebook account or not? Which of the two presidential candidates should I vote for in an American federal election? Will I get infected or not in a disease epidemic? Under what conditions does my choice or opinion become the popular one? The answer to each of these questions depends not only on the individual in question, but also crucially on their social or physical contacts with other individuals. Formulating this observation mathematically in terms of both local-contact-based binary decision-making processes and the concept of social network structures has led to many simple paradigmatic models, such as the voter model and the susceptible-infected model, that scientists study in order to understand how behaviors, opinions, and infectious diseases spread among human populations.