OpenTripPlanner (OTP) is the leading open source platform for multimodal trip planning and transportation network analysis. It provides both a web interface and an Application Programing Interface (API) for third-party applications, allowing users to search for itineraries including pedestrian, bike, transit, and car components. OTP relies on open data standards: the General Transit Feed Specification (GTFS) for transit schedule data, OpenStreetMap (OSM) for street network information, and GTFS-Realtime for vehicle position, delay, and alert data. OpenTripPlanner (OTP) is an open source platform for multi-modal and multi-agency journey planning. It follows a client-server model with several map-based web interfaces included and exposes a REST API that can be used by third-party applications. OTP is fully multi-modal in that access to transit and transfers can occur on foot or by bicycle accounting for one-way streets, bicycle lanes, or the hilliness of terrain. OTP relies on open data standards including GTFS for transit and OpenStreetMap for street networks. In the new version of OTP currently under development, GTFS-Realtime updates are applied during the itinerary optimization process so late or cancelled vehicles are taken into account. Launched in 2009, the project has attracted a thriving community of users and developers. It has received investment from public agencies, startups, and transportation consultancies alike. Originally supported by Portland Oregon's TriMet agency, who now use OTP as the basis of their regional trip planner, web-based OTP deployments now exist around the world and OTP is also the routing engine behind several popular smartphone applications.