AWS Step Functions is a managed service offered by Amazon Web Services (AWS) that enables the creation of serverless workflows and state machines for the execution of complex distributed applications. These workflows are defined using Amazon States Language, a JSON-based language that describes the states, transitions, and inputs/outputs of the workflow. The states can represent various types of operations, such as AWS service integrations, Lambda function invocations, wait states, and error handling. The transitions between the states are determined based on the inputs and outputs of each state and conditions specified in choice states. This book explains some of the difficult concepts that discourages using AWS serverless services.