This document discusses linear, abelian, and continuous groups and how relaxing these properties leads to more complex groups. It begins with the simplest group, the real numbers R, and progresses to integer lattices Z and Z^n, then non-abelian Lie groups like SL(n,R). Lattices in these groups like SL(n,Z) are discussed, along with properties like the congruence subgroup property. Open questions are raised regarding the irreducibility of random matrices and deciding membership in subgroups of SL(n,Z).