Celestia is the first modular data availability network, introducing a new paradigm in blockchain architecture by separating the consensus and data availability layers from execution. Rather than processing transactions itself, Celestia provides a scalable data availability layer that other blockchains (rollups) can use to publish and verify their transaction data. This modular approach allows rollup developers to deploy sovereign chains with their own execution environments while relying on Celestia for secure, scalable data availability. The network uses Data Availability Sampling (DAS), which allows light nodes to verify data availability without downloading entire blocks, enabling the network to scale as more light nodes join. Celestia's Blobstream bridges data availability attestations to Ethereum and other chains. The project was co-founded by Mustafa Al-Bassam and has become foundational infrastructure for the modular blockchain thesis.