We introduce an end-to-end model for participatory budgeting grounded in social choice theory. Our model accounts for the interplay between the two stages commonly encountered in real-life partici- patory budgeting. In the first stage participants pro- pose projects to be shortlisted, while in the second stage they vote on which of the shortlisted projects should be funded. Prior work of a formal nature has focused on analysing the second stage only. We in- troduce several shortlisting rules for the first stage and analyse them in both normative and algorith- mic terms. Our main focus is on the incentives of participants to engage in strategic behaviour during the first stage, in which they need to reason about how their proposals will impact the range of strate- gies available to everyone in the second stage.