k-theoretic enumerative invariants are defined by holomorphic euler characteristics of coherent sheaves on moduli spaces. in this talk, i will give an introduction to quantum k-theory whose definition involves moduli spaces of stable maps to given target spaces. i will mention its connections to birational geometry, combinatorics, and number theory. in joint work with yang zhou, we proved wall-crossing formulas of quantum k-invariants for any orbifold git quotient. these formulas can be used to compute quantum k-invariants. when the target space is an orbifold, quantum k-theory turns out to be quite different from its cohomological counterpart--quantum cohomology. i will present some of these new phenomena.