The Heralds’ Visitations are records of visits to various places to record family genealogies, changes to families, made by the College of Arms heralds. They can provide useful information, but any researcher has to understand that the information is fallible. Just because it was recorded three centuries ago, Aunt Agatha’s information about the family is as likely to be misleading then as now. I had a great aunt who authoritatively told me that one of my female great-great-great aunts was a doctor working for the Rothschild family. In fact, she was a nurse working for the Rothschild family, so she was partly right. The problem is always to know which bit of the information is correct!
So with the proviso that one needs to be sceptical about information without supporting facts, there are more and more Heralds’ Visitations available on the Internet Archive, which is a great resource for family historians. The main difficulty for this set of documents, as for many others with large series, is distinguishing which edition you’re looking at without a lot of clicking in and clicking out of the individual documents. I have therefore compiled a link list of those I have found so far:
The visitations of England can provide a wealth of information for the family history researcher. The visitation from 1893 contains not just family history information but also in some cases portraits and silhouettes. It’s worth searching quite carefully.
You will find interesting background information on the Herald’s Visitations on the mediaeval genealogy site here.