Stacks (STX) is a layer built on top of the Bitcoin blockchain, designed to expand the functionality of Bitcoin by enabling smart contracts and decentralized applications (dApps). It aims to make Bitcoin more than just a passive asset by unlocking its potential for use in sophisticated applications. Stacks uses a consensus mechanism known as Proof of Transfer (PoX), which allows it to connect with the Bitcoin blockchain, thereby benefiting from Bitcoin's robust security. The Stacks layer is designed to be scalable, enabling transactions that settle on Bitcoin. It uses the Clarity programming language, which is designed for safety and predictability, allowing developers to know with certainty what a contract will do before it executes.

Stacks operates by using the Bitcoin blockchain as its base layer. It introduces its own consensus model, known as Proof of Transfer (PoX), which allows users to transfer the base currency (BTC) to mine STX. This mining mechanism effectively bootstraps the security of the Stacks blockchain using BTC. All transactions on the Stacks layer are automatically hashed and settled on the Bitcoin blockchain, providing an additional layer of security. Stacks also uses the Clarity programming language for smart contracts, which is designed for safety and predictability. This allows developers to know with certainty what a contract will do before it executes.

Stacks aims to unlock the potential of Bitcoin for use in a variety of applications. It enables the creation of smart contracts and decentralized applications (dApps) that can use Bitcoin as an asset and settle transactions on the Bitcoin blockchain. Potential use cases include decentralized finance (DeFi) applications, non-fungible tokens (NFTs), and more. For instance, developers can build applications that require fully-expressive smart contracts, high performance, or greater privacy. Stacks also enables atomic BTC swaps and assets owned by BTC addresses, further expanding the potential use cases for Bitcoin.

The Stacks project was initiated in 2017 by Muneeb Ali, who had just completed his PhD. His thesis laid the groundwork for the Stacks layer for Bitcoin. The original whitepaper was released the same year, and the project gathered substantial support. Prior to this, the early team had been building protocols and apps on Bitcoin before they began working on Stacks. In 2019, Stacks conducted the first-ever SEC qualified token offering for the general public, including the US. From 2018 to 2020, the team focused on building out the Stacks infrastructure, which is a programming layer for Bitcoin. The Stacks cryptocurrency has a predefined supply that is set to reach approximately 1,818 million STX.