The Books of Assumption contain a unique survey of the income of church properties in Scotland (Argyll and the Isles apart) in the 1560s, driven by the characteristic imperative to document, and thus secure, revenue in a time of turmoil. The historian, following in the footsteps of the tax-gatherers, is offered a window through which to explore the wider world of the resources which sustained the church.

The late medieval church was the largest organisation and the wealthiest single landowner in the Scottish kingdom, with an annual income ten times that of the crown. The Books of Assumption were compiled for the crown in the expectation that a share of the church's riches might be reallocated to augment the finances of both the royal household and the reformed church which had just come into being.

The Books of Assumption document in detail the distribution of the church's wealth drawn from a thousand parishes and a population of 800,000 living mainly in small rural communities, and form a record akin to the Valor Ecclesiasticus of England. This is a huge and fascinating database of importance for historians of all interests.