Programmers aspire to produce reusable code. This is one of the great goals in object-oriented coding. We like to abstract useful functionality from the messiness of specific context, turning a particular solution into a tool that can be used again and again. To come at this from another angle, if programmers love the reusable, they hate duplication. By creating libraries that can be reapplied, programmers avoid the need to implement similar solutions across multiple projects. Even if we avoid duplication in our own code, though, there is a wider issue. For every tool you create, how many other programmers have implemented the same solution? This is wasted effort on an epic scale: Wouldn’t it be much more sensible for programmers to collaborate and to focus their energies on making a single tool better, rather than producing hundreds of variations on a theme? In order to do this, we need to get our hands on existing libraries. But then, the packages we need will likely require other libraries in order to do their work. So, we need a tool which can handle downloading and installing packages, as well as manage their dependencies. That is where Composer comes in; it does all this and more besides.