AdMob Mediation allows apps to serve ads from multiple sources, including AdMob and third-party networks, to maximize fill rates. There are two types of mediation campaigns: impression goal campaigns and networks ordered by eCPM. Mediation requires integrating third-party SDKs and configuring networks in the AdMob UI. Over 30 networks are supported through SDK-based or SDK-less mediation. Proper setup in AdMob, third-party dashboards, and the app code is needed to implement AdMob mediation.