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# Modules

LangChain provides standard, extendable interfaces and external integrations for the following modules, listed from least to most complex:

#### [Model I/O](/docs/modules/model_io/)
Interface with language models
#### [Data connection](/docs/modules/data_connection/)
Interface with application-specific data
#### [Chains](/docs/modules/chains/)
Construct sequences of calls
#### [Agents](/docs/modules/agents/)
Let chains choose which tools to use given high-level directives
#### [Memory](/docs/modules/memory/)
Persist application state between runs of a chain
#### [Callbacks](/docs/modules/callbacks/)
Log and stream intermediate steps of any chain
