Electrons and ions have been used for over 40 years as probes to investigate the fascinating properties of helium liquids. The study of the transport properties of microscopic charge carriers sheds light on superfluidity, on quantum hydrodynamics, on the interactions with collective excitations in quantum liquids. The structure of the probes themselves depends on their coupling with the liquid environment in a way that gives further insight into the microscopic behavior of the liquid in different thermodynamic conditions, such as in the superfluid phase, in the normal phase, or near the liquid-vapor critical point. This book is a comprehensive review of the experiments and theories about the transport properties of charge carriers in liquid helium. This is a subject about which no such other reviews are devoted. The book is intended for graduate and postgraduate students and for the specialists who will benefit of its completenes and accuracy.