An Ethereum client is a software application that implements the Ethereum specification and communicates over the peer-to-peer network with other Ethereum clients. Different Ethereum clients interoperate if they comply with the reference specification and the standardized communications protocols. While these different clients are implemented by different teams and in different programming languages, they all “speak” the same protocol and follow the same rules. As such, they can all be used to operate and interact with the same Ethereum network.
Ethereum is an open source project, and the source code for all the major clients is available under open source licenses (e.g., LGPL v3.0), free to download and use for any purpose. Open source means more than simply free to use, though. It also means that Ethereum is developed by an open community of volunteers and can be modified by anyone. More eyes means more trustworthy code.
Ethereum is defined by a formal specification called the “Yellow Paper” (see “Further Reading”).
This is in contrast to, for example, Bitcoin, which is not defined in any formal way. Where Bitcoin’s “specification” is the reference implementation Bitcoin Core, Ethereum’s specification is documented in a paper that combines an English and a mathematical (formal) specification. This formal specification, in addition to various Ethereum Improvement Proposals, defines the standard behavior of an Ethereum client. The Yellow Paper is periodically ...
