Affiliate marketing involves affiliates promoting a brand's products and only getting paid a commission when a sale is made. It is a large industry worth billions. Affiliate networks help track affiliate activity and payments for most brands that do not have their own tracking technology. Using an affiliate agency can help when a campaign is large, traffic volumes are high, multiple networks or regions are involved, or optimization is needed. Proper communication, listening to affiliates, providing the right creative assets and data, and preventing duplicate payments are some tips for success. Affiliate marketing's goal should be reaching incremental sales through affiliates rather than cannibalizing own efforts.