Poortmannen is a Dutch family-history website dedicated to researching and sharing information about the Poortman surname and its different family branches in the Netherlands. It introduces the history of several Poortman lineages, each with its own founding ancestor, and notes that there are around 20 distinct Poortman families in the country. Visitors can explore an online genealogical database, use its search function, and consult statistics and research materials to investigate ancestors, family connections, places of residence, occupations, marriages, and children.

The site highlights two branches in particular. The Mülheim Poortman line traces its ancestry to Jorgen Niklas Poortman, whose descendants settled in the Netherlands, especially in Maassluis and the surrounding area. Another section examines the Poortman family in De Wijk, in southwest Drenthe, drawing on genealogies recorded in the early nineteenth century by land surveyor Willem Koops; this branch identifies Albert Hilberts as its founding ancestor. The website is presented as an ongoing research project, with information continually being updated.