Perfect binding / saddle stitch / spiral

Saddle stitch nests folded sheets inside each other and staples through the fold. Cheapest, thinnest, page count must be a multiple of 4, and it stops behaving somewhere past 64 to 80 pages. Perfect binding stacks the pages, grinds the spine, glues it into a wrapped cover: this is the paperback look, and it is the only one of the three that gives you a printable spine (whether there is enough spine to print on comes from the calculated spine width, which is page count times paper caliper plus the cover, not from a page-count rule of thumb). Spiral punches holes and threads one continuous plastic or metal coil through them; wire-o punches the same holes and clamps a double-loop wire comb shut through them. Both lie dead flat and fold all the way back, which is why cookbooks, manuals and workbooks use them.

Choose by page count first, then by how the thing gets used. Under 40 pages and cheap, saddle stitch. A book you want on a shelf with a readable spine, perfect binding. Something that has to stay open on a counter or a music stand, spiral. Hardcover work (case bound, Smyth sewn) is the upgrade above all three.

Gotcha: both of the folded formats eat your margins. Saddle stitch suffers creep, where inner spreads push outward and lose outer margin at the trim, so the middle of the book gets cropped differently than the outside. Perfect binding swallows 3 to 6mm into the glued spine that no amount of flattening recovers. Lock the binding spec before you set margins, never after, and keep faces and critical content off the gutter.