The reaction of 1-butene over ferrierite has been studied by C-13 MAS NMR. It is shown that extensive double bond isomerisation and the formation of dimers, mainly dimethyl-hexenes and trimethyl-pentenes, dominate the early catalytic events. Strong interactions between the butene double bond and the Bronsted acid sites shift and broaden the butene olefinic signal extensively. The olefinic carbon signals of isobutene and butene dimers are not observed in these experiments because of the interactions mentioned above and the effect of carbon scrambling. At higher reaction temperatures, the formation of isobutene dominates the spectra and this catalytic event parallels the consumption of 3,4,4-trimethyl-2-pentene. It is suggested that that 3,4,4-trimethyl-1-pentene isomerises to 2,4,4-trimcthyl-1-pentene which in turn, rapidly cracks to form isobutene. At higher reaction temperatures, isobutene undergoes extensive secondary reaction leading to C-1-C-5 paraffins and aromatic coke.