What polygon can be tessellate?

Regular polygons: Equilateral triangles, squares, rectangles, rhombi, hexagons. Irregular polygons: Isosceles triangles and symmetric trapeziums (isosceles triangles with the odd angle cut off by a line parallel to the base) will do if they are alternating up and down. There are also many irregular shapes. MC Escher (see for example, http:/www.mcescher.com/Gallery/gallery-symmetry.htm) used repeated irregular shapes to tessellate. Although some of these have curved sides, they can be replaced by appropriate straight sides to produce polygons which will do the trick.