Some titles simply don’t exist as ebooks. Generally, ebook versions are most commonly available for publications printed in the last decade or two. Digitised books scanned by institutions are usually significantly older, to be safely out of copyright. This means that a great deal of 20th-century books in particular are not available except in print.
Some publishers provide ebooks for individual private purchase only because that model is the most effective for them financially. An ebook being available for you to purchase via Amazon, say, does not automatically mean that the library can buy a copy. We will always do our best to try to find an institutional copy to buy, but sometimes there simply will not be one.
Some publishers have not licensed their ebooks for sale in the UK market. In some cases it might be possible to purchase an institutional ebook in, say, North America, but not here (and the reverse is likely to be true too).
Cambridge University Libraries use approved suppliers and platforms for ebook supply, to ensure ongoing and secure access. Sometimes an ebook will only be available on an insecure platform, which we cannot use.
Similarly, some ebooks are not hosted on a secure platform but must be downloaded and hosted locally. Like most universities, we do not have a local repository for bought ebooks (the Apollo repository is for Cambridge research output only), so this is not an option for us.
Sometimes an ebook is available but its price makes its purchase impractical for us. We will always try to find a solution, negotiating with providers and sometimes bringing multiple library budgets together to afford a book, but we might have to turn a request down. Your faculty/departmental library staff should be able to help you try to find alternatives.
On a similar note, sometimes a specific title is only available through the purchase of (or subscription to) a much bigger ebook package. Library staff then need to work with academic staff and students to ascertain whether the larger package would be useful and provide value for money, and whether relevant budgets can support the costs.
Finally, sometimes an ebook which Cambridge has got access to might not be available to you because it is already in use (you will normally see the message “all available copies currently in use”). Huge numbers of ebooks can be used by unlimited numbers of readers at the same time, but some are more restricted and might, for example, have a single-user access model. You will need to wait until the ebook is “free” again before you can access it.