Generally speaking, Utility Patents protect useful, novel, inventive (a.k.a. "non-obvious") subject matter.

At least in the United States, patentable subject matter can include nearly anything related to a human-caused transformation, for example, a:

• "Process"
  • that is, a novel method of transforming nearly anything,
  • the method can involve manufacturing, engineering, chemistry, biology, business, information, or software
  • e.g., an innovative method for transforming iron into steel, or a new method of transforming accounting data into a tax return

• "Article of Manufacture"
  • that is, a new good resulting from a transformation,
  • e.g., a device, such as an innovative light bulb, mouse trap, or modem

• "Composition of matter"
  • that is, a new material resulting from a transformation,
  • e.g., a new chemical compound, drug, or gene sequence

• "Machine"
  • that is, a novel system for causing a transformation,
  • e.g., an innovative machine for making a new or old device

Assuming that a beneficial use for the invention can be identified (other than acting as a boat anchor or paperweight), nearly every invention is considered "useful" from the patent law perspective.

Also, while an invention might seem "obvious" from a layperson or engineer's standpoint, US patent law is quite strict about what must be proven before an invention can be deemed "obvious" from a patent law perspective.

Thus, the initial concern is in determining if an invention is "novel". The answer to this question can often be found via a Patentability Search.