Over the years, influencer marketing has gone from a nice-to-have to must-have when it comes to marketing strategy. The momentum influencer marketing has picked up isn’t slowing anytime soon – the industry is expected to be valued at $21.1 billion this year, according to Influencer Marketing Hub, a resource for the industry.

From the rise of micro influencers to updated guidelines from the Federal Trade Commission, keeping up with the changes isn’t an easy task. Once-hot trends have cooled off, replaced in some cases by a yearning for more authenticity.

For a comprehensive look at the ups and down of the influencer marketing industry, find what’s in and what’s out below. And let us know what we missed.