In 2021, online advertising will represent for the first time in history more than half of total ad spending. According to Zenith's Advertising Expenditure Forecasts, web advertising will account for 52 percent of global ad spending, as compared to 44 percent in 2018 and a projected 47 percent in 2019. However, the growth of online advertising is expected to slow down, from a 17 percent increase in 2018 to 9 percent in 2021. The growth of web advertising is driven by online videos and social media, which are expected to register respective average annual increases of 18 and 17 percent from now to 2021.