Maassen is a surname. Notable people with the surname include:
Frans Maassen (born 1965), Dutch cyclist
Friedrich Maassen (1823–1900), German jurist
Hanns Maaßen (1908–1983), German journalist and writer
Hans-Georg Maaßen (born 1962), German politician and lawyer
Nol Maassen (1922–2009), Dutch politician
Peter Maassen (1810–1890), German entomologist
Peter J. Maassen, American jurist
Sascha Maassen (born 1969), German racing driver
Theo Maassen (born 1966), Dutch comedian and actor
Wolfgang Maassen, German philatelist
Xavier Maassen (born 1980), Dutch racing driver