The agile practice is only one of the many iterative methods devised by development leaders in the past. Fundamentally speaking, iterative methods opposed the overly-incremental approach of the waterfall method by using a multitude of smaller phases. These phases encompass the main parts of the waterfall method (requirement, design, implementation, verification, and maintenance); but done so in smaller, more frequent increments. These are also called 'mini-waterfalls'. In essence, the agile practice moves through a life cycle of the waterfall development method in a much shorter amount of time. The 'thought leaders' behind the formation of the agile development practice refined it using 12 key principles. These principles will be discussed in Chapter 7 - The 12 Agile Principles, and will be applied in most of the lessons throughout this eBook.