London's Plus-Minus Ensemble, often called simply Plus-Minus, is an ensemble specializing in contemporary music, often in music using experimental techniques such as open instrumentation. The group is responsible for a wide range of premieres of contemporary pieces. Plus-Minus was formed in 2003 by composers Joanna Bailie and Matthew Shlomowitz. The pair plays various instruments as needed. The other members of the ensemble are pianist and accordionist Mark Knoop, who also serves as conductor, clarinetist Vicky Wright, pianist (and Messiaen specialist) Roderick Chadwick, electric guitarist Tom Pauwels, violinist Marcus Barcham-Stevens, and cellist Alex Waterman. Plus-Minus was named after a 1963 work of the same title by Karlheinz Stockhausen. That work features open instrumentation: it can be realized by any instruments in ensembles of various sizes. Plus-Minus has made a specialty of such works, performing not only the Stockhausen piece but Louis Andriessen's Workers Union (1975, "for any loud sounding group of instruments") and Cornelius Cardew's Treatise. Plus-Minus has premiered many contemporary works, including those by Øyvind Torvund, Erik Ulman, and Lawrence Crane. The group has also performed other pieces of a primarily conceptual nature and has explored works with electroacoustic instrumentation. Plus-Minus has been featured on series all over Europe devoted to contemporary music; these include Open Ear on BBC Radio 3, the Sampler Sèries festival in Barcelona, and Copenhagen's Klang Festival. The group's 2019-2020 calendar includes the Warsaw Autumn festival. In 2019, Plus-Minus moved in the direction of collective management, with Knoop and Wright joining Bailie and Shlomowitz as co-directors. The group has given workshops at various British institutions, as well as at Stanford University in California, and in 2019 it was named Ensemble-in-Residence at the Reid School of Music at the University of Edinburgh. That year, Plus-Minus released its debut album on the NMC label, featuring Bailie's Artificial Environments for field recordings, vocal narrator, and chamber ensemble.