Film is today widely used by many historians to investigate past and present social, cultural and political currents. Film historians make use of the traditional primary source materials—production records, scripts, trade journals, the diaries and memories of film-makers, and publicity records such as box-office sales and film reviews—but the main sources for film historians are the films themselves. This creates a unique dilemma, because films are complex cultural texts that are in many ways different from traditional historical sources such as letters and government records or even traditional literary texts such as novels. As such the analysis of film requires specialist methods and skills that are unique to film history.