In this talk, we will demonstrate the novel role of surgeries along embedded tori in four-manifolds in (1) relating homeomorphic but not diffeomorphic four-manifolds, and in (2) producing new infinite families of pairwise non-diffeomorphic four-manifolds within the same homeomorphism class, as well as families of smoothly knotted but topologically unknotted surfaces. Meanwhile, we are going to unfold the strong affiliation of round handles with smooth four-manifolds.