While I have been growing 'cut-and-come-again' vegetables for quite some time, it was only in the last few years when I came across that expression. It describes exactly what comes to mind: you cut off just as much as you need and let the remainder of the plant to continue to grow. The plant will grow to replace what you have cut, so that you can continue to harvest fresh vegetables for weeks on end. Leafy greens are best suited to this kind of harvest, though some herbs are also amenable to this kind of growth.
Cut-and-come-again vegetables can be sown early in the growing season, and often benefit from cooler weather for germination. For more information on when to best sow these vegetables, you can check out the detailed regional planting charts of West Coast Seeds.
Be sure when harvesting that you aren't pulling or yanking on your plant. You might just end up ripping the whole thing out! Use your garden or kitchen scissors to snip off what you need.
Check out the slideshow above for my garden favourites, including chard, lettuce, spinach, kale, arugula, corn salad, pack choi, and herbs (cilantro, basil, parsley).
Other miscellaneous cut-and-come-again vegetables include:
Amaranth, beetroot (top greens), chicory, endive, mizuna, mustard, radicchio, sorrel. Similar to other leafy greens, the outer layer of leaves can be removed and the hearts can be left to grow and mature, producing even more tasty leaves!