Oleg Dmitriyevich Kononenko (Russian: Олег Дмитриевич Кононенко) is a Russian cosmonaut. He has flown to the International Space Station three times, as a flight engineer for Expedition 17 aboard Soyuz TMA-12, as a flight engineer on Expedition 30 and commander of Expedition 31 aboard Soyuz TMA-03M, and as a flight engineer on Expedition 44 and Expedition 45 aboard Soyuz TMA-17M. Kononenko has accumulated over 533 days in orbit during three long duration flights to ISS.

Mikhail Borisovich Kornienko (Михаил Борисович Корниенко; born 15 April 1960) is a Russian cosmonaut. Kornienko served as a flight engineer on the International Space Station during Expedition 23/24 and was selected along with Scott Kelly for a year-long mission aboard the ISS.

Valery Grigoryevich Korzun (Russian: Валерий Григорьевич Корзун, born 5 March 1953) is a Russian cosmonaut. He has been in space twice totalling 381 days. He has also conducted four career spacewalks.

Oleg Valeriyevich Kotov (Russian: Олег Валериевич Котов) was born on October 27, 1965, in Simferopol, Crimean oblast in the Ukrainian SSR. After a career as a physician assigned to the Soviet space program, he joined the Russian cosmonaut corps. He has flown two long duration spaceflights on the International Space Station logging just short of a year in space. Most recently, Kotov flew on the Soyuz TMA-10M/Expedition 37/Expedition 38 long duration spaceflight, from September 2013 until March 2014.

Vladimir Vasiliyevich Kovalyonok (Belarusian: Уладзі́мір Васі́льевіч Кавалёнак; Russian: Влади́мир Васи́льевич Ковалёнок; born March 3, 1942 in Beloye, Minsk Oblast, Belorussian SSR, is a retired Soviet cosmonaut. He entered the Soviet space programme on July 5, 1967 and was commander of three missions. He retired from the cosmonaut team on June 23, 1984.

Konstantin Mirovich Kozeyev (Russian: Константин Мирович Козеев) is a retired Russian cosmonaut. He flew as Flight Engineer on Soyuz TM-33 in 2001.

Sergei Konstantinovich Krikalev (Russian: Серге́й Константинович Крикалёв, also transliterated as Sergei Krikalyov; born August 27, 1958) is a Russian cosmonaut and mechanical engineer. As a prominent rocket scientist, he is a veteran of six space flights and ranks third to Gennady Padalka and Yuri Malenchenko for the amount of time in space: a total of 803 days, 9 hours, and 38 minutes.

Valeri Nikolayevich Kubasov (Russian: Вале́рий Никола́евич Куба́сов; 7 January 1935 – 19 February 2014) was a Soviet/Russian cosmonaut who flew on two missions in the Soyuz programme as a flight engineer: Soyuz 6 and Soyuz 19 (the Apollo–Soyuz mission), and commanded Soyuz 36 in the Intercosmos programme. On 21 July 1975, the Soyuz 7K-TM module used for ASTP landed in Kazakhstan at 5:51 p.m. and Kubasov was the first to exit the craft. Kubasov performed the first welding experiments in space, along with Georgy Shonin.

André Kuipers is a Dutch physician and ESA astronaut. He became the second Dutch citizen, third Dutch-born and fifth Dutch-speaking astronaut upon launch of Soyuz TMA-4 on 19 April 2004. Kuipers returned to Earth aboard Soyuz TMA-3 11 days later. Kuipers is the first Dutch astronaut to return to space. On 5 August 2009, Dutch minister of economic affairs Maria van der Hoeven, announced Kuipers was selected as an astronaut for International Space Station (ISS) Expeditions 30 and 31. He was launched to space on 21 December 2011 and returned to Earth on 1 July 2012.

Aleksandr Ivanovich Laveykin (Russian: Александр Иванович Лавейкин; born April 21, 1951) is a retired Soviet cosmonaut. Born in Moscow, Laveykin was selected as a cosmonaut on December 1, 1978. He flew on one spaceflight, for the first part of the long duration expedition Mir EO-2. He flew as a flight engineer, and was both launched and landed with the spacecraft Soyuz TM-2. He spent 174 days 3 hours 25 minutes in space. Married with one child, Laveykin retired on March 28, 1994. Launched in February 1987, his spaceflight was intended to last until December 1987, but doctors on the ground determined that he was having minor heart irregularities. For this reason, in July he was replaced by Soviet cosmonaut Aleksandr Pavlovich Aleksandrov, who stayed on Mir to the end of the expedition in December.

Vasily Grigoryevich Lazarev (Russian: Васи́лий Григо́рьевич Ла́зарев; February 23, 1928 – December 31, 1990) was a Soviet cosmonaut who flew on the Soyuz 12 spaceflight as well as the abortive Soyuz 18a launch in April 5, 1975.

Aleksandr Ivanovich Lazutkin (Russian: Александр Иванович Лазуткин; born October 30, 1957) is a Russian cosmonaut.