Writing code is absolute fun -- it just takes the 3C's: coffee, coke, cool hardware (used to be cigarettes back in the day) -- but delivering working, tested, documented, modular, resistent, secure, accepted, installed, software to a client, profitably, is a totally different bowl of fish -- it takes not just knowledge in several fields of coding, it also takes a lot of organization to keep everything together, on schedule, and within budget. And it simply gets harder, the larger the project, and more resources (ie, people) are needed to deliver the goods.

To help manage this potential chaos several procedural 'recipes' have been proposed -- they are, as a group, called Software Development Life Cycles. 

Many system/software development life cycle (SDLC) models have been created over the years (eg: waterfall, fountain, spiral, build and fix, rapid prototyping, incremental, synchronize and stabilize, etc.), but the two most commonly in use these days are:

• the Waterfall Method (the original SDLC)
• the Agile Method (a newer SDLC).

Each one has its pros and cons, its advocates and detractors.