10.1. Introduction

An addition process is where something adds across a π-bond.  When the first elementary step in the process is an electrophilic addition step, that name is applied to the whole process also.
The most common examples of electrophilic addition are seen with alkenes and alkynes, since these are relatively electron-rich. For example:
The electrophilic addition elementary step is nearly always followed by a coordination step, where the carbocation combines with a nucleophilic group to form the final addition product. The electrophilic addition step is rate-determining, because an unstable carbocation intermediate is formed.  If the attacking electrophile has an available lone pair, it can lead to cyclic intermediates; these reaction are covered in section 10.7.
Electrophiles that work well for simple additions are usually proton donors (Bronsted-Lowry acids), such as hydrogen halides and other strong acids:
Note: Aromatic ring compounds like benzene do not undergo additions that go to completion; they are greatly stabilized by the aromatic delocalization, and this would be destroyed by an addition.
Video by Martin Walker introducing electrophilic addition