| KIDD (Cyril) | The Irish mail [nd] | Railways |
| KIDD (Cyril) | Newfoundland: travelling post office cancellations [1987] | Railways |
| KIDD (Cyril) | A Christmas story. Light is shed on the ‘Posted in Advance’ scheme for delivery on Christmas Day | N/A |
| KILLEEN (Kenneth AL) | World War 1 – 1914 to 1918 “The Great War” – The prisoner of war ships [1993] | Maritime, Military, POW |
| KIMPTON (L) | Airmails across the Middle East 1918-1930 [2015] | Aviation |
| KIMPTON (Laurence) | British Commonwealth Pacific Airlines 1946-1954 [2005] | Aviation |
| KING (M) | Newark on trent. A history of its past [1985] | N/A |
| KING-FARLOW | The postmarks & provisional stamps of the Faroe Islands: some further observations [1947] | N/A |
| KINGSTON (R A) | Camp postmarks of the United Kingdom: an illustrated reference book of postmarks from military and naval establishments [1971] | Maritime, Military |
| KIRBY (Ron J) | The skeleton handstamps of Cumbria [1993] & Second Edition [1998] | N/A |
| KIRK (Reginald) | Australian mails via Suez 1852 to 1926 [1989] | Maritime |
| KIRK (Reginald) | British maritime postal history Vol. 1 The P.& O. Bombay & Australian Lines 1852-1914; Vol. 2 The P.& O. Lines to the Far East [1981] | Maritime |
| KIRK (Reginald) | The postal history of the P&O service to the Peninsula [1987] | Maritime |
| KIRYUSHKIN (A V) | List of post offices in the Russian empire | Russia |
| KIRYUSHKIN (A V) | Russian postmarks an introduction and guide [1989] | Russia |
| KIRYUSHKIN (A V) | Russian railway postmarks [1994] | Railways, Russia |
| KLEMPKA R. | Foreign Military Activity in the Russian Civil War 1917-1923 (2019) | Military, Russia, WW1 |
| KLING (Georges) | Histoire de la poste et du timbre en Nouvelle-Caledonie et dependances [1983] | N/A |
| KNEITSCHeL (Rudolfo) | Matasellos utilizados en las estafetas ambulantes ferroviarias Argentina 1865-1892 [1987] | N/A |
| KNIBBELER (Thieu) | Gelderse monumenten reeks: postkantoren [1994] | N/A |
| KNIGHT (D R) & SABEY (A D) | The Lion Roars at Wembley: The British Empire Exhibition 1924-1925 [1984] | Exhibitions |
| KNIGHT (R C) | The postmarks, postal routes & principal postage rates of Southern Rhodesia to 1984 [1984] | N/A |
| KNOPKE (Karl) | A short guide to Jamaican postmarks: translated by P E Robinson | N/A |
| KOFMAN (Victor) | The Odessa post (fragments of history) edited by Vsevod Furman [1998] | N/A |
| KOHLER (Gunter H) | Post und tram: postbeforderung mit strassenbahnen in Deutschland und in ausland [1998] | N/A |
| KOLEKSIYONU (Alexander) | Ottoman post in Palestine 1840-1918 vol 2 [2007] | N/A |
| KONWISER (H M) | United States stampless cover catalog [1936] | N/A |
| KONWISER (Harry M) | Texas Republic postal system: a brief story relating to the post office & postal markings of the Republic of Texas [1933] | N/A |
| KORTEWEG (P C) | 300 jaar aanwijzingen postmerken & poststempels in Nederland 1570-1870 [1957] | N/A |
| KORTEWEG (P C) | Postdienst en poststempels hier te lande tot 1811 [1941] | N/A |
| KOTTELAT (Marcel) | Studie uber die Schweizerische hotelpost [1995] | N/A |
| KOURI (Yamil HJR) | The postal history of Spanish New Orleans [2004] | N/A |
| KRIEBEL (William Victor) | Correio aereo: a history of the development of air mail service in Brazil [1996] | Aviation |
| KRONENBERG (Alb A) | Catalogue of a private collection of books on philately and postal history [1965] | N/A |
| KRULL (Johan) | Suomen laivaleimat [1991] | N/A |
| KRUPNICK (Jon e) | Pan American’s Pacific pioneers: a pictorial history of Pan Am’s Pacific first flights 1935-1946 [1997] | Aviation |
| KUCHARSKI (Jerzy) | The postal history of the Polish Field Post Offices in the Holy Land 1940-1947 [1981] | Military |
| KUMPF-MIKULI (Anton) | Die postempel [1978] | N/A |
| KURCHAN (Mario D) | Argentine postal history: study of forged cancellations, forerunners & maritimes 1760-1870 [1976] | N/A |
| KURCHAN (Mario D) | Historia postal maritima Argentina / Argentina maritime postal history [1994] | Maritime |
| KURCHAN (Mario D) | Historia postal maritima de Rio de la Plata: Republica oriental del Uruguay / The River Plate maritime history [1996] | Maritime |
| KURCHAN (Mario D) | Rutas y tarifas de los correos aereos en Sudamerica 1928-1940…Air mail routes and rates in South America [1999] | Aviation |
| KURCHAN (Mario D) | Los secretos de las rutas y tarifas aereas en sudamerica 1928-1941 – The secrets of air mail routes & rates in South America [2001] | Aviation |
| L'UNION POSTALE UNIVERSELLE (UPU) | Les actes de l’Union Postale Universelle 3 vol | N/A |
| L'UNION POSTALE UNIVERSELLE (UPU) | Nomenclature internationale des bureaux de poste, 4 vol | N/A |
| LAAKSO (J-R) | Across the oceans – Development of overseas business information transmission 1815-75 [2007] | N/A |
| LAMPART (I D) | St Helena Boer prisoners of war censor & camp handstamps | Military, POW |
| LANDER (J G C) editor | Malta: post offices in the north [1973] | N/A |
| LANDER (J G C) editor | The postal history & markings of Cospicua, Paola, Zejtun & Zurrieq [1972] | N/A |
| LANDER (J G C) editor | The postmen’s handstamps of Malta [1972] | N/A |
