How do I identify a spider?

Spider identification is difficult even for experts. There are about 4,000 species of spiders in North America alone, and there are no doubt many “new” species awaiting descriptions and names from scientists. The characters needed to identify a spider, like the arrangement of its eyes and microscopic views of its genitalia, are often not visible in images. It is helpful, however, to note the kind of web you found the spider in (not all spiders spin webs, though), whether it was outdoors or indoors, and include an accurate assessment of the size of the spider (body length or legspan). Always remember to include a specific geographic location in your post. Lastly, make sure it is actually a spider that you have, and not another arachnid, or even an insect.