Often known colloquially as montebretia, these are cormous perennials (ht 60-90 cm) from the family Iridaceae and hail from South Africa. The most commonly seen form has spikes of funnel-shaped orange flowers; it can be quite invasive, multiplying rapidly. There are a number of named forms that are supposedly less of a menace in gardens, and their massed blooms give a dazzling splash of colour in summer, in hues of orange (for example, 'Emily McKenzie'), red (for example, 'Lucifer') and yellow (such as 'Solfatare'); some are bicoloured. I am reluctant to recommend these bulbs too heartily and they should never be allowed to escape into bush areas. I try to keep mine under control by ruthlessly pulling out great handfuls of them every year and disposing of them in the green waste bin. They grow best in full sun with well-drained soil. They may need staking. They should be divided when they become congested. They look very effective grown with blue Salvia or other blue-coloured flowers. They are useful as cut flowers.
Postscript: I no longer recommend at all that these bulbs are grown in home gardens. I found that even the named versions multiplied excessively, and were also subject to foliage diseases.