We present a comprehensive review of physics effects generated by leptoquarks (LQs), ie,
hypothetical particles that can turn quarks into leptons and vice versa, of either scalar or
vector nature. These considerations include discussion of possible completions of the
Standard Model that contain LQ fields. The main focus of the review is on those LQ
scenarios that are not problematic with regard to proton stability. We accordingly concentrate
on the phenomenology of light leptoquarks that is relevant for precision experiments and …