Art History Resources
Large collection of artworks, meticulously organised by country/culture of origin, date, artist and themes.

Artstor (subscription only)
Despite the challenge of rapidly expanding Google Art Project (see below), Artstor remains a good place to browse thousands of images in high detail.

Ashmolean Museum
An eclectic range of collections. As well as the usual section on Western art, there are collections specialising in timepieces, brass rubbings, silverware and finger rings.

Avalon Project
Maintained by the Yale Law School, here you will find documents focusing on law and diplomacy from 4000 BC to the present

Bodleian Library 
Early Modern Letters Online
– Amazing collection of digitised images and manuscripts from the Bodleian Libraries Special Collections

British Library
Search the collections of the British Library for maps, images, books, datasets, sounds and printed music.

British Museum
Over 2,000,000 records of objects in the British Museum collections, most of which have images. Features objects from all around the world, dating back to prehistoric times.

Convict Transportation Registers Database
Information on more than 123,000 of the 160,000 convicts transported to Australia between 1787 and 1867 . From the UK National Archives.

Electronic Enlightenment
60,000 documents of edited correspondence from the 17th-19th centuries, linking over 8000 people across Europe, the Americas and Asia. Letters discuss everything from religious tolerance to animal rights, vulcanology to classical archaeology, economic modelling to celebrity culture. Maintained by the University of Oxford’s Bodleian Libraries.

Ghetty Research Institute
Digitised manuscripts, books, prints and photos from the archives of the Ghetty Research Institute. Major collecting areas include: alchemy, festivals, orientalist photography, artists’ letters and sketchbooks.

Google Art Project
Over 40,000 high-resolution images of artworks ranging from oil-on-canvas to sculpture and furniture; constantly expanding.

Google Books
Digitised texts from university and specialist libraries all over the world. Genres other than fiction are well represented, with travelogues, historiographies, advice manuals, pamphlets and so on. Texts are downloadable as PDF and EPUB files; alternatively, they are viewable online in an intuitive format. Note: only the texts which are out of copyright are available as free downloads.

Google Ngram Viewer
This tool scans an immense number of books to tell you whether a word was in use at a particular time, and can also show you the relative popularity of words over time.

Internet History Sourcebooks Project
Primary sources for the following categories: African history, East Asian history, Indian history, Islamic history, Jewish history, history of science, women’s history, and gay and lesbian history. Special collections include traveller’s accounts and legal history. Run by Fordham University.

JSTOR (subscription only)
Online collection which specialises in digitising the main humanities periodicals, usually covering all issues from the journal’s foundation to the most recent output.

Library of Congress
The LoC’s digital collections offer a huge range of print, pictorial and audio-visual resources, ranging from – to name just a few examples –  historic American newspapers, to early sound recordings and photography, to the papers of famous individuals. (Note: do not confuse with the online library catalogue).

Los Angeles County Museum of Art
Images of art and textiles from all over the world, spanning a wide historical period.

Pitt Rivers Museum
The Pitt Rivers Museum at the University of Oxford features archaeological and anthropological collections from all over the world. The online collection covers objects, manuscripts, photographs, sound and film.

Victoria and Albert Museum
Images of over a million objects and 500,000 art and design related images.

Weekday calculator
Find out what day of the week it was, for any date in any year.

Wikipedia illuminated manuscripts
Fairly wide selection of images from (mostly medieval) illuminated manuscripts. Useful if you need to find an image quickly, as the collection is very clearly organised by subject, century and country.