This thesis summarizes the results of several phylogenetic studies of birds included in the “higher land bird assemblage” (Anomalogonatae sensu Beddard 1898). The phylogenetic analyses are primarily based on gene sequences obtained from the nuclear genome (exons of the c-myc and RAG-1 genes and an intron of the myoglobin gene).  Monophyly of the “higher land bird assemblage” has previously been suggested based on the loss of the ambiens muscle in these birds. However, in agreement with other molecular studies, the results presented do not corroborate the monophyly of this group, although the tree is basically unresolved to due lack of statistical support (Bootstrap, parsimony jackknifing and Bayesian inference). Of the groups included in the “higher land bird assemblage”, Strigiformes (owls), Apodiformes (swifts and hummingbirds), Coliiformes (mousebirds), Trogoniformes (trogons), Piciformes (e.g., woodpeckers, barbets, toucans, puffbirds, jacamars) and Passeriformes (passerines) are supported as monophyletic, whereas Caprimulgiformes (e.g., nightjars, oilbird, and owletnightjars) and Coraciiformes (e.g., rollers, cuckoo-rollers, bee-eaters, kingfishers, hoopoes, hornbills) are not. Among the caprimulgiform birds, the owlet-nightjars (Aegothelidae) are found to be closer to the swifts and hummingbirds (Apodiformes) than to other caprimulgiforms.  In addition, the results indicate that the cuckoo-roller (Leptosomatidae) is not associated with rollers and ground-rollers as suggested by some previous studies. Instead, the rollers and ground-rollers (Coracioidea) are probably sister group to a clade containing todies, motmots, kingfishers, and bee-eaters (Alcedini). Hoopoes, woodhoopoes, and hornbills are monophyletic (Bucerotimorphae). As in many previous analyses, the relationships between Strigiformes, Apodiformes, Coliiformes, Trogoniformes, Piciformes, Passeriformes, Leptosomatidae, Coracioidea, Alcedini, and Bucerotimorphae are unresolved, which could indicate that these groups underwent a rapid evolution, probably in the late Cretaceous – early Tertiary.