The results of a comprehensive small-angle X-ray scattering study of linear polyethylene crosslinked using a peroxide have been combined with a study of the crystallization kinetics to obtain a generalized picture of the effects of limited mobility and comonomer content on crystallization. It is shown that there are three regions of behaviour : (i) an initial region in which the crosslinks are soluble in the crystal to a certain limiting composition; (ii) a region in which the lamellar thickness decreases in a continuous manner with increasing crosslink density; and (iii) a region where the lamellar thickness is virtually independent of crosslink density. The results are interpreted using the Sanchez-Eby theory, the Andrews theory and regime theory to generate a comprehensive description of the behaviour.