The reproductive behaviour of the pigeon was studied in pairs which were allowed free access to each other only once a day, during a 34 minutes' observation period. The different actions typical of reproductive behaviour are described. The most important of these are bowing, attacking intention, attacking, driving, nest demonstration, moulding, nibbling, pushing, begging, billing, displacement preening, pecking, squatting, strutting, mounting, copulation, collecting of nest material, nest-building and nest defence. Bowing, attacking and driving are most frequent at the beginning of the cycle, but a new peak in the frequency of bowing and attacking occurs in the male at the time the female begins to show nest demonstration and pushing. Nest demonstration is more frequent in the male than in the female at the beginning of the cycle. In the female it occurs later, but reaches almost the same frequency as in the male. Nibbling occurs only in the female at the beginning of the cycle, but later on it is also shown by the male. Pushing, which is also shown mainly by the female, is most frequent during the days immediately prior to egg-laying. At this time the collecting of nest material also reaches its peak. This behaviour is more frequent in the male than in the female. Begging, billing and displacement preening are frequent during the whole pre-incubation period. Apart from squatting and mounting, displacement preening, begging and billing were more closely associated with copulation than any of the other actions studied by us. The sequence in which the dominance of different behaviour elements occurs during the proceeding of the cycle is, more or less, repeated during the individual 34 minute encounters. The courtship actions do not form rigid chains. Each activity may be followed or preceded by several others, but often the association with some particular activities predominates. There are two dominating sequences of activities, one leading to copulation through displacement preening and billing, and another leading to nibbling and collecting of nest material via nest demonstration. The actions that compose the courtship pattern seem to form three fairly distinct groups. The first of these is the primarily aggressive behaviour, represented by bowing, attack intention and attacking. Driving seems to be more closely associated with this group than with any other. The second group is sexual behaviour proper, consisting of displacement preening, begging, billing, squatting, mounting and copulation. The third group is formed by nest demonstration, pushing, collecting of nest material and nest-building. Transition from one behaviour group to another occurs on occasions when there is a change of motivation or of external stimulus situation. When the behaviour pattern changes from one type to another, behaviour is often seen which contains elements of two different actions. All intermediate stages between ordinary preening and displacement preening are seen. The function and origin of some of the courtship actions is discussed. Bowing, which is primarily an intimidating display belonging to aggressive behaviour, also has a sexual function in some cases. It contains ritualized elements of attack intention and of braking movements, elicited by the activation of escape tendencies at the approach of the opponent. Driving seems to be an ambivalent behaviour, during which the male is both aggressively and sexually motivated. It may be derived from the intention movements of attacking and of mounting. The most important functions of nest demonstration are to attract the female to the nest site, to strengthen the bond between the partners and suppress aggressiveness, and to stimulate the collecting of nest material in the male. Of the elements which compose the nest demonstration, nodding is probably derived from the movement used when adding material to the nest. Wing vibration is very similar to the movements of the wing shown by the young when begging for food from the parents. Aggressive behaviour seems to have a stronger inhibitory effect on nest demonstration than on sexual behaviour, and since aggressive behaviour is most frequent in the first part of the cycle as well as at the beginning of the individual tests, nest demonstration occurs comparatively late. 34 minutes of daily contact between male and female during a period of 12 to 15 days was sufficient to produce broodiness and egg-laying.