I have been told that no one should apply for a patent without the help of a lawyer and that any inventor who does so is foolishly risking making a mistake that could cost him or her dearly. But I have six patents under my belt, and I wrote them and applied for all of them myself. I've been through pretty much the whole gamut of U.S. Patent Office travails: rejections, (successful) appeals, and even that rare event--a patent reissue. Much as I revel in being a distinctive and unique individual, I don't believe I possess a special aptitude, and I think most inventors would benefit from writing their own patents.

Consider the following:

It is very unlikely that your invention (despite its brilliance) will ever be commercially successful, since only about one in 1000 is, so any mistakes on the application probably won't matter.

Most patents held to be invalid were drafted by attorneys, so a lawyer is not a silver bullet against risk. Among other problems, attorneys can fail to understand the invention adequately and thus make claims that are too broad or too narrow.

Doing the work yourself--known legally as acting pro se --will save you a lot of money.

Drafting a patent application is challenging, but for those with an engineering turn of mind, it's also a great deal of fun. The most important part of writing a patent is drafting patent claims that are broad enough to make your invention something that other people should license while making the claims narrow enough to establish the invention's unique and useful nature.

Before you even consider drafting a patent application, you must do a patent search. It is very likely that someone has thought of--and patented--your idea first. In years past, I spent many hours in the U.S. Patent Office, perched uncomfortably on a radiator in the public stacks, perusing boxes of crumbling patents. Now, however, you can do Internet searches from the comfort of your own home or office, knowing that every patent is online.

The first step in conducting a search is to classify what it is you have invented. Look in the government classification manual to find the class and subclass that apply to your invention. The manual is available online at http://www.uspto.gov/go/classification/uspcindex/indexs.htm.

Let's walk through a typical search. Suppose you have an idea for a new type of digital tone-detection filter. Under the broad class "F" you will find filters. You will note that electrical filters are mostly in class 455 but that in class 708, subclasses 300+ refer to electrical digital filters. The classes and subclasses are hyperlinked to the descriptions. Clicking on the "300+" leads to a list of subclasses 300 through 323, entitled "Electrical computers: arithmetic processing and calculating." Subclass 312 refers to tone detection.

The next step is to search the patent database at http://patft.uspto.gov/netahtml/search-adv.htm. To search on class 708, subclass 312, enter: ccl/708/312 and click "search." This will bring up all U.S. patents that have class 708, subclass 312, as a primary or secondary classification. The point of doing the search in this somewhat recherché manner is that it will produce a much shorter and more apropos list of results than simply attempting to search the text of patent applications using keywords such as "filter" or "detector."

Once the list of relevant patents appears, clicking on the patent number brings up the entire patent. Patent drawings are in an obscure version of the TIFF format that requires your browser to have an appropriate plug-in for viewing, which can be a headache. For example, Apple's QuickTime plug-in will display the images when installed in Internet Explorer but not when installed in the Firefox Web browser. But a very good plug-in, AlternaTIFF, available free at http://alternatiff.com, enables Firefox to display the images.

Read all the relevant patents. Even if you are fortunate and no patent anticipates your idea, you still have some reading to do. Read some patents in your invention's primary and secondary classifications to get a feel for the language that's used. Pay particular attention to the claims. The goal in drafting claims is to make the first set of claims as general as the patent examiner will allow and then to list additional, dependent claims that more narrowly define the scope of your patent. Note the terms used in previous patents and consider using the same terms in your application.

Also pay attention to the format of the patents. Most follow the same basic structure: title, abstract, specifications, drawings, and claims. You can get software, such as PatentEase, published by Inventorprise Inc., Vestal, N.Y., that will help you construct and format your patents correctly. However, the results, automatically generated from filling in on-screen forms, often require a lot of manual work to get them to a point where they will be acceptable. Instead of using software, I suggest looking at a number of published do-it-yourself guides to drafting patent applications and other helpful reference works.