The Shelley phase, or Shelley era, is the second of five stages in the published development roadmap of the Cardano blockchain. Activated by a network upgrade on 29 July 2020, it introduced proof-of-stake delegation, allowing holders of ADA to stake their coins with independent stake pools and earn rewards, and began moving the production of blocks from federated nodes run by Cardano's founding organisations to pools operated by the community.
Shelley followed the Byron phase, which launched the network in 2017 with basic transfers, and preceded the Goguen phase, which added smart contracts. The roadmap is completed by eras named Basho, focused on scaling, and Voltaire, focused on governance. The coin itself is covered under Cardano (ADA), and the eras are named after figures from literature and science.
The Shelley phase in plain terms
Imagine a new town whose founders ran the town hall themselves for the first few years, keeping the records and approving every change. Shelley was the point at which they began handing over the record-keeping to elected local offices run by residents. Anyone could set up an office, and residents could back the office they trusted with their votes, earning a small reward for taking part.
The founders did not leave at once. They reduced their own share of the work step by step until the residents' offices were doing almost all of it.
What Shelley introduced
- Stake pools. Operators run nodes that produce blocks. Each pool registers on-chain, sets its fees and can pledge its own ADA to signal commitment.
- Delegation. ADA holders can delegate the voting weight of their coins to a pool without handing over the coins themselves. Funds stay in the holder's wallet, can be spent at any time and are not locked.
- Rewards. Each epoch, lasting five days, rewards from a reserve and from transaction fees are shared among pools and their delegators according to performance and stake.
- New address types. Addresses gained a part linked to staking rights, separating who can spend coins from who controls their stake.
- Consensus. The network moved to a version of its Ouroboros protocol, the Ouroboros Praos design, in which slot leaders are chosen privately in proportion to stake.
Cardano's delegated staking does not use slashing: pools that perform badly earn less, but delegators do not lose principal.
How the transition worked
The change was carried out using the hard fork combinator, a technique developed for Cardano that lets the chain switch rules while keeping a single continuous history, rather than splitting into old and new chains. Before the upgrade, an "incentivised testnet" launched in late 2019 let would-be pool operators practise and earn rewards based on a snapshot of their holdings.
After the switch, a setting called the decentralisation parameter controlled what share of blocks still came from the federated nodes run by IOHK, the Cardano Foundation and Emurgo. It was lowered in steps over the following months, and by March 2021 all blocks were produced by community stake pools.
Effects
Shelley quickly attracted thousands of registered stake pools and a large share of ADA delegated to them, which Cardano's supporters cited as evidence of broad participation. The design shaped later projects, including the initial stake pool offering, in which new projects ran pools and paid delegators in their own tokens. In late 2020 the network raised a parameter that sets the target number of pools, to spread stake more evenly.
Shelley also laid groundwork for later eras. Its ledger rules introduced the idea of protocol parameters that can be changed by on-chain update proposals, and its address format and multi-signature scripts were extended in 2021 by the Allegra and Mary upgrades, which added time-locks and native tokens, so that new assets could be created on Cardano without smart contracts. These intermediate upgrades are sometimes counted as part of the Shelley period and sometimes as a bridge to Goguen. For many ADA holders, Shelley was the first point at which owning the coin brought a direct, regular income, which changed how the asset was marketed and held, and how exchanges offered staking services to customers.
Criticism and limitations
Critics noted that, during Shelley, Cardano still had no smart contracts, so staking was its main use, and that much of the network's activity was rewards rather than real economic use. Others point out that a large share of delegation goes to a limited number of pool operators and to pools run by exchanges, and that some operators run many pools, which weakens the effect of the target-pool setting. Supporters reply that the absence of lock-ups and slashing makes participation unusually easy for ordinary holders. The phased roadmap itself has been criticised for slow delivery, while defenders argue its research-led, peer-reviewed approach reduces the risk of serious bugs.