  A linac (linear accelerator) is a system that allows to accelerate charged
particles through a linear trajectory by electromagnetic fields. This kind of
accelerator finds several applications in fundamental research and industry.
The main devices used to accelerate the particle beam will be introduced in the
first part of the paper, while in the second part, the fundamentals of the
longitudinal and transverse beam dynamics will be highlighted. A short
paragraph is finally dedicated to radiofrequency quadrupoles (RFQ).
