Since 2018 The Search Network has been publishing an annual Search Insights report which is a set of short essays on a wide range of issues broadly (but not totally) related to enterprise search. Search Insights 2021 can be downloaded free-of-charge, and with no requirement to register, from the web site of The Search Network. As well as the essays the report includes a list of search vendors, an extensive glossary and a list of books and blogs on search topics. [Disclosure – I am a member of the Network]