A Domain-Specific Language (DSL) is a programming language specifically designed for a particular (narrow) domain. DSLs can increase the productivity of programming in many ways: by offering concise programming notations, reducing the number of defects, improving communication between developers and business experts, and so on. DSLs as part of software development pipelines are slowly becoming more and more popular. One reason for the increased popularity is tooling: modern language workbenches – tools to define DSLs together with their IDEs – make developing new languages cost-effective and fun. In this tutorial, I will talk about language workbench JetBrains MPS. It supports projectional (structured) editing, which is an alternative to mainstream text-based editing that allows overcoming the limits of language parsers and enables domain experts to program. JetBrains MPS allows defining DSL editors supporting textual, tabular and graphical notations. During the tutorial, the participants will implement an IDE for a trivial Entities Language. The tutorial is intended for those interested in implementing domain-specific languages, and requires basic programming skills in Java or another object-oriented programming language.