We examine the implications of audit-firm cross-border integration for client-firm tax planning in a unique setting: the formation of PwC Europe in 2012, an alliance of local member firms of the PwC network in Central Europe. Our study is the first to provide empirical evidence of the role of audit-firm networks in facilitating client-firm cross-border tax planning and to document the importance of audit-firm cross-border integration for client-firm tax-motivated income shifting.