Ad optimization is a process which helps to choose better performing ads for display. Better performing ads generate more revenue, more clicks, more conversions, a higher click-through ratio, or a higher conversion ratio. Optimization will result in higher ROI for better ads. Revision, improving or deactivation of irrelevant or poor ads can also be done. The goal of optimization is to maximize the yield from a pool of ads. The yield metrics can be clicks, conversions, click-through ratios or conversion ratios. This optimization process begins with creative, then shifts to placements and individual publishers, and finally to a campaign-wide level. Optimization can be performed on a pre-flight phase, during a campaign, or after a campaign is over. Optimization should be done at the most granular level so that easy corrections are taken into account before making sweeping campaign management changes. Numerous third-party platforms enable brands and agencies to optimize their media buying known as Optimization Engines. These ensure that an ad is delivered where it should be according to consumers, advertisers, and available websites. There is Buy-side optimization for advertisers and Sell-side optimization for publishers. Ad exchanges help in the process of Ad optimization using the DSP and SSP platforms.