WebDC3 is a web interface working on top of SeisComP3 standard seismological services (http://geofon.gfz-potsdam.de/software/webdc3/). It is AJAX-based and allows users to conveniently discover seismic stations and explore events in seismic catalogues, build and submit requests for data and metadata and finally download the results in different formats. Requests can be built using either absolute time windows or by station-event combinations suitable for different data processing pipelines. Furthermore, data requests and downloading of their results can be made in separated steps, allowing for larger requests and better supporting users with low bandwidth or unstable connections. WebDC3 functions in the style of a previous webdc service implemented at GFZ. The new web interface runs as a Python web application using the Web Server Gateway Interface (WSGI). It has been adopted by a number of seismic agencies. Source code is freely available for download; its use is governed by the "GNU General Public License, Version 3, 29 June 2007"