String concatenation is the process of joining multiple strings together to form a single string. It is a fundamental operation available in virtually every programming language.

In JavaScript, strings can be concatenated using the + operator, concat() method, or template literals (`${}`). For joining many strings, Array.join() is more efficient. JavaScript string processing books cover the trade-offs between these approaches.

In Python, the + operator, f-strings, and ''.join() are commonly used. Repeated concatenation with + in loops creates new string objects each time, which can impact performance.

When concatenating strings, ensure character encodings match. Mixing encodings can cause garbled text. Programming fundamentals books treat string operations as an essential topic.