The notion of linear series, or $g^r_d$'s (collections of cuts of a given variety by hyperplanes), is critical in algebraic geometry, where it yields a rich theory in which both classical and modern techniques beautifully come together. In this seminar we discuss some of the basic tools of this theory, and how they provide us with a better understanding of the geometry of algebraic curves. If time permits, a geometric interpretation of the Riemann-Roch theorem involving linear series on curves will be discussed.