Data on the political opportunity structure (POS) in 7 Western European countries (Austria, Belgium, Ireland, Netherlands, Spain, Switzerland, and United Kingdom) between 1990 and 2009. A number of indicators are included to cover generic and issue-specific political opportunity structures (immigration-related) at the party level. The data were collected as part of the FP7-funded project Support and Opposition to Migration (http://www.som-project.eu/