The title of this book – ‘Brethren in Christ’ – is taken from the addresses used in many, if not most, of the letters exchanged during the first half of the seventeenth century between Calvinists who were active in congregations across Europe as elders and ministers, and their, more often than not, unknown colleagues within the sister communities they contacted. The term testifies to the strong sense of identity and belonging of these early modern Calvinists. They had no doubt that they belonged to an easily identifiable group of brethren, signified solely by their faith, and independent of their nationality and culture. They saw themselves as belonging to a group of people whom God had elected as His chosen people – the new Covenanters. As such their obligation was first and foremost to other godly Calvinists, irrespective of their nationality and abode. They were convinced that any other allegiances had to be subordinated to this, their primary duty.