Abstract: Functionality is described herein for allowing an investigating user to explore event sequences. The functionality constructs an expression in a pattern-matching language in response to the user's interaction with a user interface presentation. The functionality then compares the specified expression against one or more event sequences to find portions of the event sequences that match the expression, if any. The comparing operation yields matching sequence information. The functionality then generates and displays output information based on the matching sequence information. In one case, the expression is a regular expression.