Publishers
- M Press (media) Ltd. 2
- M. & J. Hobbs 4
- 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.J. Finnis 1
- M.M. Holloway 1
- Mabecron Books 1
- MacDonald 15
- MacDonald & Co. 1
- Macdonald & Co. (Publishers) Ltd. 7
- MacDonald & Evans Ltd. 1
- Macdonald and Jane's 9
- MacDonald Children's Books 1
- Macdonald Futura Publishers Ltd. 1
- Macdonald Orbis 1
- Macdonald Purnell 1
- MacGibbon & Kee 2
- Mackie & Co. Limited 3
- Maclehose Press 1
- MacMillan 46
- Macmillan & Co. 36
- Macmillan & Co. Ltd. 153
- Macmillan Children's Books 33
- Macmillan London Limited 12
- MacMillan Press 1
- Macmillan Press Ltd 4
- Macmillan Publishing Co. 9
- Macmillan Publishing Co. Inc. 1
- Macmillan, New York 1
- Madison Press Books 1
- Maeght Editeur 1
- Magdalen College 3
- Magna Books 1
- Magna Press 1
- Magnard 1
- Magpie Publishing 2
- Mainline & Maritime Ltd 2
- Mainstream Publishing 6
- Mainstream Publishing Company (Edinburgh) Ltd. 2
- Mallard Books 1
- Mallard Press 2
- Malta Ornithological Society 1
- Mamelok Press 2
- Mammoth 3
- Manas Publications 1
- Manchester University Press 12
- Manning 1
- Mantle Oral History Project 1992 1
- Marcel Dekker 4
- Marcus Harris & Lewis Ltd. 5
- Marcus Ward & Co. Limited 1
- Margaret K. Mcelderry Books 1
- Margo 1
- Marine Media Management 1
- Mariner Press 1
- Maritime Books 2
- Maritime Publications 1
- Marjory Lester 1
- Mark + Moody Limited 1
- Mark Baker 1
- Markosia Enterprises Ltd. 2
- Marks & Spencer 2
- Marks and Spencer Limited 1
- Marlborough College 2
- Marshall Brothers 1
- Marshall Harris & Baldwin Ltd. 1
- Marsilio 1
- Marston House 1
- Martin Bairstow 1
- Martin Robertson 1
- Martin Secker 2
- Martin's Printing Works 1
- Martinus Nijhoff 3
- Marvel Comics Limited 1
- Marvel Entertainment Group 2
- Mascot Media 1
- Maskew Miller 2
- Mastercraft Printing 1
- Mastiff Club Of America 1
- Matador 4
- Mathematical Optimization Society 1
- Mathern Parochial Church Council 1
- Matrix Design 1
- Matthew S. Batham 1
- Matthiesen Fine Art 1
- Maurice Temple Smith Ltd 1
- Max Parrish 7
- Max Parrish And Co Ltd 2
- Max Reinhardt 5
- Maxiprint 2
- Maxwell J. Roberts 1
- Mayflower Books 1
- Mazzoleni 1
- Mbi Publishing 17