The photolysis of gaseous 1-pentene was carried out in a static system using the krypton resonance line at 123.7 nm (10.0 eV) at pressures in the range 0.5 – 400 Torr (0.7 – 533 hPa). Only decomposition processes were studied and no attempt was made to establish the pattern of free radical reactions. The major dissociation products observed were ethylene, allene, propylene, 1,3-butadiene, acetylene, propyne and 1-pentyne. The minor products included methane, ethane, propane, someC5H8 and C4H6 hydrocarbons, and 1-butene. The radical species were identified using scavengers such as oxygen, H2S and HI. The pressure dependence of the yields of the major radicals (C3H5, CH3, C2H5, C2H3, C3H7, and C4H7) was established. The C2H, C4H5,CH2 and C3H3 radicals were found to be unimportant. The primary decomposition channels are established. The cleavage of a CH bond occurs with yield of φ = 0.34 ± 0.06 and the cleavage of a CC bond occurs with nearly the same yield of φ = 0.39±0.06. The CC bond breaks mainly in the position which is β to the double bond; some contribution (φ = 0.06) is due to a rupture in the γposition which yields stable C4H7 radicals. All four primary intermediates, i.e. C5H9, C3H5, C2H5 and H, are energized. The radicals either decompose (isomerization prior to decomposition is possible in some cases) or undergo collisional stabilization; some hydrogen atoms add to the double bond prior to thermalization. The contribution of ionic processes to the formation of low molecular weight products is slight. Some details of the secondary processes are established but the overall mechanism is too complex to be fully unravelled.