John Richards wrote Landsknecht Soldier for Osprey Publishing in 2002, it is illustrated by Adam Hook.
Richards describes how the Holy Roman Emperor Maximilian I had ordered the creation of these mercenaries with the intention of them boosting the imperial armies.
This tome explains the reasons why the best places to hire or recruit these soldiers where in the German states, Burgundy (which Maximilian and his heirs ruled) as well as the cantons of the Swiss Confederation. These areas of Europe produced some of the toughest soldiers on the European continent, which made them ideal for the purposes of the monarchs who hired them.
The Landsknecht were all tough soldiers that were generally loyal to their comrades if not the people that actually hired them. Richards describes how they often dressed in a unconventional fashion to distinguish them from other fighting men.
He notes with surprise that the Reformation did not disrupt these units as much as it should have done. It might have been assumed that the Protestants amongst the Landsknecht soldiers would have refused to serve in the armies of Roman Catholic rulers, especially those of the Holy Roman Emperor Charles V. However the majority of Protestant Landsknecht troops had few scruples in serving in the ranks of the imperial Habsburg armies whether or not they were fighting against Protestant or Roman Catholic enemies. Charles V was content that Protestant troops to fight for him.
Richards then goes on to describe the decline of these mercenaries, brought about by new weapons and tactics had drastically reduced their usefulness prior to their disbandment in 1590.
He mentions that they were not particularly popular as civil authorities within the Holy Roman Empire plus the Swiss Confederation banned them from their territories. Ill discipline, lack of money, and a failure to keep up to date ended the usefulness of the Landsknecht.