We describe a new approach to the canonical decompositions of 3–manifolds along
tori and annuli due to Jaco–Shalen and Johannson (with ideas from Waldhausen) –
the so-called JSJ–decomposition theorem. This approach gives an accessible proof of
the decomposition theorem; in particular it does not use the annulus–torus
theorems, and the theory of Seifert fibrations does not need to be developed in
advance.