"Among the Elephants" by Iain and Oria Douglas-Hamilton (parents of Saba Douglas Hamilton-wildlife TV presenter on Big Cat Diary-UK).
Iain D-H did the first systematic study of elephants' behaviour in the wild and the book outlines his work and living with his young family for five years in Lake Manyara National Park in Tanzania. It's a fascinating book and a great starter before you read any of Cynthia Moss's books. I believe her study of the elephants in Amboseli takes up/follows on from Iain D-H's work. Interestingly it was thought five years was ample time to learn all there was to learn about wild elephants but Cynthia Moss's long term study has shown that not to be the case.
It's an old book first published in 1975 by Collins & Harvill press and first issued by Fontana in 1978 - the book (ISBN) number is 0 00 634993 5
If you like your elephants... this is a must read.