  A pedagogical review of the past 50 years of study of resonances, leading to
our understanding of the quark content of baryons and mesons. The level of this
review is intended for undergraduates or first-year graduate students. Topics
covered include: the quark structure of the proton as revealed through deep
inelastic scattering; structure functions and what they reveal about proton
structure; and prospects for further studies with new and upgraded facilities,
particularly a proposed electron-ion collider.
