There are multiple ways to configure Docker container environment variables: 1) use the ENV instruction in Dockerfile; 2) pass using -e or --env parameters during docker run; 3) use --env-file to read environment variables from a file; 4) use environment or env_file in docker-compose.yml. Environment variable priority: docker run -e > docker-compose.yml > Dockerfile ENV. Best practice: use environment variables to configure parameters for different environments (development, testing, production), avoid hardcoding sensitive information into images. For sensitive information, it's recommended to use Docker Secrets (Swarm) or Kubernetes Secrets.