Whenever software is developed based on contracts with binding agreed conditions it is exposed to risks; conditions such as the delivery of a clearly defined functional scope at a fixed price and at an agreed delivery date. Many of these risks can be mitigated by the principles of agile development. Being able to navigate projects within all agreed parameters requires cost estimation methods to be integrated into planning and controlling processes. In order to prevent these methods from eroding the advantages of agile development, they must be rapidly applicable - ideally automatable - and allow for self-calibration after every sprint. This book illustrates, how size metrics can be utilised profitably in software development processes oriented towards agile values. It points out differences and restrictions, how the accuracy of cost estimations can be increased with each sprint and examines the feasibility of automated measurements.