In soccer, the need for direct observation of tactical behaviour has led to continuous technological advances in motion recording software. Here we present SoccerEye, a sports-specific software tool to observe and record the behaviour of soccer players in their natural setting and in real time. The software was written in Visual Basic Express 2010 and includes the following features: computerised coding, improved-quality recording, episodic sampling, the reasurement of time, and diachronic analysis. Its configuration is well defined but allows for incorporation of ad hoc categories. Data can be exported in multiple generic formats, including the SDIS format for the analysis of interaction sequences with GSEQ software. However, by considering time and sequential decisions, SoccerEye itself tracks activity profiles and the dynamics of play. The greatest advantage of SoccerEye is the possibility to conduct diachronic analysis, which regards an event or multi event sequence in terms of change over time. This type of analysis takes into account the behaviour of a player and his or her team when facing the opponent, the space (pitch area) and time (starting time and duration) of each event, and other factors such as match status, match time, and competition stage. SoccerEye is a freeaccess user-friendly application that can be used to observe a single player or an entire team while controlling over the environment in which the observation takes place. This tool will hopefully contribute to the better understanding of the dynamics of soccer play.