Opportunities and strategies for crowdsourcing in the cultural heritage sector (GLAMs), and within the National Library of the Netherlands (Koninklijke Bibliotheek, KB) in particular, are the focus of this paper by Olaf Janssen, project manager for the KB. In the first part you’ll read what crowdsourcing is, what motivates people to spend their time & money on it and how it differs from old-school voluntary work. You’ll also learn what added value and advantages it can bring, held against frequently mentioned downsides. Furthermore a number of tips for setting up and running successful crowdsourced projects are given. In part two we’ll focus on crowdsourcing within the cultural heritage sector. We distinguish six forms of crowdsourcing within GLAMs, each illustrated by a number of examples. Using these six categories, we evaluate why & how the National Library of the Netherlands could use the time and expertise of the crowd to add value to its online activities. The entire article is crowded with examples of crowdsourcing projects, both outside and inside GLAM-territory.