The melting and crystallization behaviour of metallocene-catalysed commercial poly(ethylene-co-octene) was investigated by conventional and temperature-modulated differential scanning calorimetry (d.s.c. and TMd.s.c.) and by temperature-resolved wide angle X-ray scattering. The thermal behaviour of the copolymer is characterized by a very broad melting and crystallization range. Both the melting and the crystallization are complex transitions of at least two processes with different kinetics. On decreasing the temperature, crystallization starts with the formation of a separate crystalline phase and continues gradually with development of an amorphous-crystalline mesophase until the glass transition is reached. In TMd.s.c., the formation of the crystalline phase is seen as an irreversible, non-reversing process, whereas the glass transition gives a reversing heat flow signal. Similarly, on heating, the melting process is initiated after traversing the glass transition as a largely reversing process, followed by melting of the crystalline phase with non-reversing character in a narrower temperature range.