In this thesis we prove two major \(ZJ\)-type group-theoretic results before generalising them to the category of fusion systems. We also study alternative proofs of the fact that when a fusion system \(F\) on a finite \(p\)-group \(P\) is sparse and \(p\) is odd or \(F\) is \(S\)\(_4\)-free, \(F\) is constrained.