LangChain —LLMChain Introduction

4 min readFeb 14, 2024

What is Chain in LangChain?

In LangChain, a “chain” refers to a sequence of components or steps that are linked together to process input and generate output, especially in the context of working with language models. It is a conceptual framework used to organize and streamline the interaction between different elements involved in handling language tasks.

For developing more complex applications, it’s essential to connect various components and functionalities of LangChain through a “Chain” — linking models together or connecting models with other components.

The concept of interlinking multiple components to form a chain is straightforward yet powerful. It simplifies the implementation of complex applications and makes them more modular. This approach enables the creation of unified, coherent applications, thereby easing debugging, maintenance, and enhancement.

The implementation and use of chains in LangChain are quite straightforward.

  • First, LangChain utilizes well-designed interfaces to implement specific functionalities of a chain. For example, the LLM Chain (LLMChain) is capable of receiving user input, formatting it using a PromptTemplate, and then passing this formatted response to the LLM. This effectively encapsulates the entire Model I/O process within the chain.
  • Second, once the specific functionalities of a chain are implemented, we can build more complex chains by combining multiple chains or integrating a chain with other components. Thus, internally, a chain encapsulates a series of functionalities, while externally, it can be linked and combined with others. Essentially, a chain can be viewed as a fundamental functional unit within LangChain.

Foundational Chains

There are two foundational chains:

  • LLMChain
  • SequentialChain


The LLMChain is the simplest and most fundamental chain built on large models. It includes a prompt template that formats user input, feeds the…