Social media has garnered a large share of firms' advertising budgets over the past several years. However, the channel faces growing headwinds. Marketers, publishers, and adtech firms should read this report to understand how social advertising spend will evolve over the next five years across 25 European countries on PCs and mobile devices as well as for banner and video ads. We also estimate Facebook's share of social ad spend in each country. A downloadable forecast model accompanies this report online.