Structured programming is a programming paradigm characterized by source code that uses block-based source code structure to encode control flow such as sequence, selection (i.e. if-then-else and switch) and iteration (i.e. for and while).

Originally, the central goal of the structured programming movement was to eliminate the need for and use of the goto statement. As goto provides powerful and flexible flow control, it can be used to write any arbitrarily complex algorithm, but the resulting code often has significant quality issues, commonly described as spaghetti code. Structured programming replaces goto with constructs that tend to result in better code. The paradigm became popular and for the most part achieved the goal of supplanting goto. In fact, its ubiquity is so thorough that for much of software development, it is simply the way code is written, no longer a topic of discussion as it once was.

Structured programming is sometimes associated with modular programming even though they are different. In a general sense, structured implies a sense of modularity and of being written to be efficient and easy to understand and modify, but this is not what structured programming means in a narrow sense.

After structured programming became popular, the style of programming that preceded it was retroactively called non-structured programming. Although technically a programming paradigm, it differs from other paradigms in that it was not intentionally designed. It was simply the state-of-the-art before structured programming was envisioned.

The paradigm emerged in the late 1950s with the appearance of the ALGOL 58 and ALGOL 60 programming languages, with the latter including support for block structures.

Contributing factors to its popularity and widespread acceptance, at first in academia and later among practitioners, include the publication of what is now known as the structured program theorem in 1966, and the publication of the influential "Go To Statement Considered Harmful" open letter in 1968 by Dutch computer scientist Edsger W. Dijkstra, who coined the term structured programming.

The structured program theorem provides the theoretical basis of structured programming. It states that three ways of combining programs—sequencing, selection, and iteration—are sufficient to express any computable function. This observation did not originate with the structured programming movement; these structures are sufficient to describe the instruction cycle of a central processing unit, as well as the operation of a Turing machine. Therefore, a processor is always executing a "structured program" in this sense, even if the instructions it reads from memory are not part of a structured program. However, authors usually credit the result to a 1966 paper by Böhm and Jacopini, possibly because Dijkstra cited this paper himself. The structured program theorem does not address how to write and analyze a usefully structured program. These issues were addressed during the late 1960s and early 1970s, with major contributions by Dijkstra, Robert W. Floyd, Tony Hoare, Ole-Johan Dahl, and David Gries.

P. J. Plauger, an early adopter of structured programming, described his reaction to the structured program theorem: