The Lay Subsidy was a form of national taxation that was imposed by government as early as the thirteenth century. Most subsidies reveal only the monies collected, although the Tudor subsidy of 1523 -24 and other subsidies around the time are exceptions.

Subsidies were conducted and compiled for each hundred with in the county, with each hundred names of taxpayers are listed for each town or village together with the taxable amount and subsidy collected from each personm, for the town of Northampton occupations were also commonly given.

Not all subsidy returns for the county have survived. Not all adults were covered by the subsidy, so this should not be seen as a through listing of all male adults for the location covered. However, given that this subsidy pre-dates parish registers by several decades in some locations, it provides an excellent listing for genealogists and historians.

The 1523 Subsidy imposed a levy of one shilling in the pound for land worth £50, one shilling in the pound on "personaly" ie savings and personal goods. Sixpence in the pound on Capital Values over 40 shillings and less than £20. Tax was paid on whichever category gave the individual most wealth. Hence the taxable amount shown for each person does not accurately state a person's wealth but it does show a main source of it.These transcripts contain only the valuation made of the person, not the amount. Most women included in the Northamptonshire subsidy were described as Widows.

Christian names are commonly shown in Latin and abbreviated in the original , eg Robtus Willms Henncus for Robert William Henry. Where a name was unclear or obscure, curved brackets () are used to contain the uncertain part. The letter Y was commonly used in place of I and this may cause identical names to occur in different parts of the index eg, Yngran-Ingram, Aynesworth-Ainsworth.

The following words, phases and abbreviations occur throughout the subsidy, and readers are refered to Latin glossaries for clarification: