In 1973, Doyen and Wilson [7] famously solved the problem of when a 3-cycle system can be embedded in another 3-cycle system. There has been much interest in the literature in generalising this result for m-cycle systems when m > 3. Although there are several partial results, including complete solutions for some small values of m and strong partial results for even m, this still remains an open problem [4,5,8,9].The main results of this thesis concern generalisations of the Doyen-Wilson theorem for odd m-cycle systems and cycle decompositions of the complete graph with a hole. The complete graph of order v with a hole of size u, K v − K u , is constructed from the complete graph of order v by removing the edges of a complete subgraph of order u (where v ≥ u).For each odd m ≥ 3 we completely solve the problem of when an m-cycle system of order u can be embedded in an m-cycle system of order v, barring a finite number of possible exceptions. The problem is completely resolved in cases where u is large compared to m, where m is a prime power, or where m ≤ 15. In other cases, the only possible exceptions occur when v − u is small compared to m. This result is proved as a consequence of a more general result which gives necessary and sufficient conditions for the existence of an m-cycle decomposition of K v − K u in the case where u ≥ m − 2 and v − u ≥ m + 1 both hold.We prove that K v − K u can be decomposed into cycles of arbitrary specified lengths provided that the obvious necessary conditions are satisfied, v − u ≥ 10, each cycle has length at most min (u, v − u), and the longest cycle is at most three times as long as the second longest. This complements existing results for cycle decompositions of graphs such as the complete graph [1,3,10], complete bipartite graph [6,8] and complete multigraph [2].