Rinzai (or Renzai) and Soto Zen
Differences and similarities
Katinka Hesselink 2006
Zen is the Japanese version of Chinese Chan Buddhism. There are two main lineages of Zen Buddhism in Japan: Rinzai Zen and Soto Zen. Both share a disregard for the original Vinaya rules for monks and a focus on sitting meditation (Zazen).
Koans and Zazen
Both Rinzai and Soto Zen Buddhists study koans and practice Zazen. The differences are in the relative importance in day-to-day practice. To say Rinzai "stresses" koans over Zazen would be inaccurate.
It is accurate to say that Soto Zen considers the practice of Zazen to be the sole means of realization. But Soto Zen has never discarded the koan. Soto teachers lecture on koans and their students study koans outside the practice of Zazen. Soto Zen practices Zazen as awakening itself to the already realized koan. In Rinzai Zen practice, a koan is examined while sitting in order to deepen insight.
Rinzai Zen was popular in Japan amongst the Samurai, the warrior-class.
In Buddhism Monks nor Nuns marry. In fact, they have to stay celibate and practice other rigid rules, many of which sound rather strained to the modern ear. (see Pancha Sila for instance, which is only part of the rules for the monks and nuns, the Vinaya) In Japanese Buddhism though, in many lineages, the spiritual teachers do get married. Soto Zen and Rinzai Zen both have married priests. In the West both have women priests as well, though that's a Western innovation.