Google Meridian is an open source framework for Marketing Mix Modeling (MMM) designed by Google, aimed at assisting advertisers and analysts in effectively assessing the influence of their marketing initiatives across both online and offline platforms without dependence on cookies or individual user tracking. Central to Meridian is a Bayesian causal-inference model that can process aggregated data—including spend, sales, key performance indicators, reach and frequency, geographical data, seasonality, and external controls—to determine the incremental impact of each marketing channel, such as search, social media, video, and offline media, on overall results, as well as to calculate return on ad spend (ROAS), response curves, and optimal budget distribution. As an open-source tool, it affords users complete visibility into the methodologies and code, empowering them to customize model settings, data inputs, and the underlying assumptions. This level of transparency not only enhances trust but also encourages collaboration among users to refine the model further. Additionally, the open-source nature allows for community contributions, which can lead to continuous improvements and innovations in the framework.