The objective of the Nordic Workshop on Programming Theory is to bring together researchers from (but not limited to) the Nordic and Baltic countries interested in programming theory, in order to improve mutual contacts and cooperation. The 23rd Nordic Workshop on Programming Theory took place at Malardalen University, Sweden, 26-28 October 2011. The previous workshops were held in Uppsala (1989, 1999, and 2004), Aalborg (1990), Goteborg (1991 and 1995), Bergen (1992 and 2000), Abo (1993, 1998, 2003, and 2010), Aarhus (1994), Oslo (1996 and 2007), Tallinn (1997, 2002 and 2008), Lyngby (2001 and 2009), Copenhagen (2005), and Reykjavk (2006). There were 36 regular presentations at the workshop. In addition, the following four invited speakers gave presentations: Werner Damm (University of Oldenburg and OFFIS, Germany), Bjorn Lisper (Malardalen University, Sweden), Michael Williams (Ericsson AB, Sweden), and Glynn Winskel (University of Cambridge, United Kingdom).