The theory and present experimental status of parametric instabilities in CTR oriented magnetized plasmas is reviewed. Both linearized theory and the most recent non-linear theory are summarized in a compact form. The regimes of upper hybrid frequency, lower hybrid frequency, ion cyclotron frequency, Alfvén wave, and TTMP are covered. In each case the important parametric processes are discussed, including some work on the coupling to drift waves. Then recent experimental results which indicate the importance of parametric phenomena are presented.