This paper uses a rich panel dataset of Spanish manufacturing firms (1990–2006) and a propensity score reweighting estimator to show that multinational firms acquire the most productive domestic firms, which, on acquisition, conduct more product and process innovation (simultaneously adopting new machines and organizational practices) and adopt foreign technologies, leading to higher productivity. We propose a model of endogenous selection and innovation in heterogeneous firms that explains both the observed selection patterns and the innovation decisions. Further, we show in the data that innovation upon acquisition is associated with the increased market scale provided by the parent firm.