Boolean Satisfiability (SAT) can be considered a success story of Computer Science. Since the mid-90s, SAT has evolved from a decision problem with theoretical interest, to a problem with key practical benefits, finding a wide range of practical applications. From the early 60s until the mid 90s, existing SAT solvers were able to solve small instances with few tens of variables and hundreds of clauses. In contrast, modern SAT solvers are able to solve practical instances with hundreds of thousands of variables and millions of clauses. This chapter describes the techniques that are implemented in SAT solvers aiming to explain why SAT solvers work (so well) in practice. These techniques range from efficient search techniques to dedicated data structures, among others. Whereas some techniques are commonly implemented in modern SAT solvers, some others are more speciic in the sense that only some instances beneit from its implementation. Furthermore, a tentative glimpse of the future is presented.