In hardly any other area we've had as much change and improvement as in the field of databases. Just a few years ago everyone had "their" database that was used for each project. Today you are confronted with a variety of approaches and implementations. We start off with a brief look at the theoretical background of distributed systems and databases in particular. On the basis of this, we take a look at traditional relational databases such as PostgreSQL. Additionally, we dive into newer NoSQL systems like MongoDB, Redis, Cassandra, or Elasticsearch. After that, we discuss possible scenarios as well as the advantages and disadvantages of several databases: - Why SQL is in fashion (again). - Why MongoDB's document structure fits object-oriented programming so well. - How you can capture visitor hits with Redis efficiently. - Why Cassandra is so scalable and fail-safe. - How full-text search works with Elasticsearch. The right choice of database(s) hasn't become easier through the wide range of possibilities, but all the more interesting!