Node.js allows developers to easily use environment variables in their applications. Environment variables can be set globally or project-specifically using .env files. The dotenv module makes it easy to load and parse .env files, allowing developers to access variables like PORT and NODE_ENV. Node-env-run is an alternative tool that loads and initializes .env values before executing the script. If-env is a tool that allows developers to check environment variable values in npm scripts. Developers can use the DEBUG environment variable to enable verbose logging for modules using the debug module.