The round, tan, papery seeds of the cilantro plant, coriander has a warm, spicy-sweet scent and flavor that's slightly lemony, warm, and pine-y, with a whiff of caraway. One of the most common spices in Indian cuisine, it's also used in Latin American cooking, often hand in hand with cumin. Ground coriander is usually easier to find than whole seeds, but you'll get the best flavor if you buy seeds whole and grind them yourself just before using.
If you're substituting preground coriander for whole seeds; use less than what's called for whole.
Many grocery stores have a good selection of spices, but keep in mind that the most fragrant spices come from stores with a high rate of turnover.
To bring out the fragrance in coriander, toast the seeds. Put them in a dry heavy skillet and set over medium heat for a few minutes until they become fragrant. Grind the whole seeds to release the spice's flavorful aromatic oils.
Air, light, and heat are the enemies of spices, so keep them in airtight containers in a drawer or cupboard, but never over the stove.