Zenith predicts global ad expenditure will grow 4.5% in 2018, reaching US$581bn by the end of the year. Our prediction for overall growth this year has therefore not changed since June, though the growth figures have shifted for most individual markets. We then forecast 4.0% growth for 2019, followed by 4.2% in 2020 and 4.1% in 2021. Our forecast for 2019 is down slightly from our September prediction of 4.2% growth, but the 2020 forecast is stable. The 2021 forecast is new.