The web site allows search of the Herb. IMI database which contains around 400 000 records, mostly comprising specimens vouchered in the IMI fungarium (dried collection of fungi). It follows the agreement in 2009 to merge the fungal systematics expertise and resources of the Royal Botanic Gardens, Kew and CABI, including transfer to Kew of the CABI fungus collection, undertaken with financial support from DEFRA. The fungus collection, initiated in 1920 on establishment of the Imperial Bureau of Mycology, was a collaboration between seven colonial Governments to provide mycological information and expertise for pathologists and other applied biologists in the then British Empire. The collection evolved steadily over the years (undergoing a number of name changes) to become one of the leading global knowledge centres for fungal systematics, and was subsumed into CAB International in 1998. It was enhanced significantly in 1945 with the introduction of a formal accessions system, each specimen being logged in a series of ledgers and receiving a unique IMI number. Many of these were reference specimens acquired through the IMI identification service, samples being sent from CABI member countries and elsewhere for expert determination. Most of the 400 000 specimens and cultures which have passed through the IMI accessions system are vouchered, but approximately 25% were subsequently discarded as common species of minor scientific value or of inadequate quality. CABI's fungal identification service continues to this day, and a substantial number of IMI specimens are available also as living cultures maintained by CABI.

Digitization of specimen data from the IMI accessions books is now almost complete, with the assistance of funding from GBIF (2004–2005) under the DIGIT work programme. Much of the work was carried out in Cuba (including some in collaboration with a Darwin Initiative project), with a significant further proportion keyboarded in India at the NBAIM. The major task of editing and validation is ongoing as resources become available; data on this web site comprise edited but not necessarily validated data.

The combined fungal collections of RBG Kew and IMI number around 1.25 million specimens including over 45 000 types, and constitute the largest and most scientifically significant resource of its type in the world. Although the IMI fungarium formally remains the property of CABI's member countries, its curation and management (including loan administration) is now the responsibility of Kew. The Herb. IMI database is a working database, in constant upgrade and improvement. Quality of data with regard to the presence of a taxon in any particular country varies from 'high' where the record is based on material of known provenance to 'low' where a record is based on, for example, a quarantine intercept where the exact origin of the material is not available. Information in the database should not be regarded as definitive proof of the presence of a species in a particular country. Where such data are of concern, the Mycology Department at Kew (mycology@kew.org) should be consulted with regard to vouchered specimens, specialists at CABI with regard to all other aspects.