Neurobehavioural analysis of mouse phenotypes requires the monitoring of mouse behaviour over long periods of time. In this study, we describe a trainable computer vision system enabling the automated analysis of complex mouse behaviours. We provide software and an extensive manually annotated video database used for training and testing the system. Our system performs on par with human scoring, as measured from ground-truth manual annotations of thousands of clips of freely behaving mice. As a validation of the system, we characterized the home-cage behaviours of two standard inbred and two non-standard mouse strains. From these data, we were able to predict in a blind test the strain identity of individual animals with high accuracy. Our video-based software will complement existing sensor-based automated approaches and enable an adaptable, comprehensive, high-throughput, fi ne-grained, automated analysis of mouse behaviour. A utomated quantitative analysis of mouse behaviour will have a signifi cant role in comprehensive phenotypic analyses -both on the small scale of detailed characterization of individual gene mutants and on the large scale of assigning gene function across the entire mouse genome 1 . One key benefi t of automating behavioural analysis arises from inherent limitations of human assessment, namely, cost, time and reproducibility. Although automation in and of itself is not a panacea for neurobehavioural experiments 2 , it allows for addressing an entirely new set of questions about mouse behaviour and to conduct experiments on time scales that are orders of magnitude larger than those traditionally assayed. For example, reported tests of grooming behaviour span time scales of minutes 3,4 , whereas an automated analysis will allow for analysis of this behaviour over hours or even days and weeks.Indeed, the signifi cance of alterations in home-cage behaviour has recently gained attention as an eff ective means of detecting perturbations in neural circuit function -both in the context of disease detection and more generally to measure food consumption and activity parameters 5 -10 . Previous automated systems (see refs 8, 9, 11, 12 and Supplementary Note ) rely mostly on the use of simple detectors such as infrared beams to monitor behaviour. Th ese sensor-based approaches tend to be limited in the complexity of the behaviour that they can measure, even in the case of costly commercial systems using transponder technologies 13 . Although such systems can be used eff ectively to monitor locomotor activity and perform operant conditioning, they cannot be used to study homecage behaviours such as grooming, hanging, jumping and smaller movements (termed ' micromovements ' below). Visual analysis is a potentially powerful complement to these sensor-based approaches for the recognition of such fi ne animal behaviours.Advances in computer vision and machine learning over the last decade have yielded robust computer vision systems for the recognition of objects 14,15 and human actions (see Moeslund et ...