Publishers
- M Press (media) Ltd. 7
- M. & J. Hobbs 2
- M. And J. Hobbs 1
- M. Carey & Sons 1
- M. Macdonald 1
- M. Moreau 1
- M.A. Donohue & Co. 1
- M.D.E. Publications 1
- M.F. Feheley 2
- M.I.P.I. PUBLISHING 2
- M.M. Holloway 1
- Mabecron Books 2
- Mabel Esther Allan 2
- MacDonald 10
- Macdonald & Co. (Publishers) Ltd. 8
- MacDonald & Evans Ltd. 1
- Macdonald and Jane's 9
- Macdonald Futura Publishers Ltd. 1
- Macdonald Orbis 1
- Macdonald Purnell 1
- MacGibbon & Kee 2
- Mackie & Co. Limited 2
- MacMillan 36
- Macmillan & Co. 29
- Macmillan & Co. Ltd. 106
- Macmillan Children's Books 42
- Macmillan London Limited 11
- Macmillan Press Ltd 3
- MacMillan Publishers Ltd. 1
- Macmillan Publishing Co. 7
- Macmillan Publishing Co. Inc. 2
- Macmillan, New York 1
- Madison Press Books 1
- Magdalen College 3
- Magna Books 1
- Magna Press 3
- Magnard 1
- Magpie Publishing 2
- Mainline & Maritime Ltd 3
- Mainstream Publishing 3
- Mainstream Publishing Company (Edinburgh) Ltd. 2
- Mallard Books 1
- Mallard Press 2
- Malta Ornithological Society 1
- Malta University Press 1
- Mamelok Press 2
- Mammoth 3
- Manas Publications 1
- Manchester University Press 11
- Mapin Publishing 1
- Marcel Dekker 4
- Marcus Harris & Lewis Ltd. 5
- Marcus Ward & Co. 1
- Margaret K. Mcelderry Books 1
- Margo 1
- Marine Media Management 1
- Mariner Press 1
- Marion Lloyd Books 1
- Maritime Publications 1
- Mark + Moody Limited 1
- Mark O'Hanlon 1
- Markosia Enterprises Ltd. 2
- Marks & Spencer 2
- Marks and Spencer Limited 1
- Marlborough College 1
- Marrin Publishing 1
- Marshall Brothers 1
- Marshall Cavendish Children's Books Limited 1
- Marshall Harris & Baldwin Ltd. 2
- Marsilio 1
- Martin Bairstow 3
- Martin Robertson 1
- Martin Secker 2
- Martin's Printing Works 1
- Martinus Nijhoff 3
- Marvel Comics Limited 2
- Marvel Entertainment Group 1
- Maskew Miller 1
- Massey University Press 1
- Mastercraft Printing 1
- Mastiff Club Of America 1
- Matador 3
- Matilda And War Memorial Hospital 1
- Matthaus Publishers 1
- Matthew S. Batham 1
- Matthiesen Fine Art 1
- Max Parrish 6
- Max Parrish And Co Ltd 2
- Max Reinhardt 3
- Maxiprint 2
- Mayflower Books 1
- Mazzoleni 1
- Mbi Publishing 10
- McClanahan Book Company Inc. 1
- McClelland and Stewart Limited 2
- McClure, Phillips & Co. 1
- McCorquodale & Co. 3
- McCorquodale & Co. Ltd. 2
- McDonald Institute For Archaeological Research 1
- McDougall's Educational Co. Ltd. 1