Kimono, Haori, Obi, Nagajuban Seasonality Chart

Traditionally, kimono and other items are worn according to certain seasonal guidelines. Just like you wouldn't wear a wool coat in August in Texas, you wouldn't wear a lined kimono in July in Japan.

Like the Western "no white after Labor Day" rule, in recent years the strict edges of the seasons have blurred a bit as Japan's weather has grown warmer earlier in the year, but for the most part the guidelines are still followed. Here's my translation of a general chart explaining when to wear what:

The sheer fabrics are worn with a solid, opaque kimono underneath, just to be clear. ;)

If you're a kimono newbie, haori are the shorter jackets worn over kimono, and nagajuban are the underwear kimono put on first under the kimono.