  Until the last few decades, investigations of stellar interiors had been
restricted to theoretical studies only constrained by observations of their
global properties and external characteristics. However, in the last thirty
years the field has been revolutionized by the ability to perform seismic
investigations of stellar interiors. This revolution begun with the Sun, where
helioseismology has been yielding information competing with what can be
inferred about the Earth's interior from geoseismology. The last two decades
have witnessed the advent of asteroseismology of solar-like stars, thanks to a
dramatic development of new observing facilities providing the first reliable
results on the interiors of distant stars. The coming years will see a huge
development in this field. In this review we focus on solar-type stars, i.e.,
cool main-sequence stars where oscillations are stochastically excited by
surface convection. After a short introduction and a historical overview of the
discipline, we review the observational techniques generally used, and we
describe the theory behind stellar oscillations in cool main-sequence stars. We
continue with a complete description of the normal mode analyses through which
it is possible to extract the physical information about the structure and
dynamics of the stars. We then summarize the lessons that we have learned and
discuss unsolved issues and questions that are still unanswered.
