Are the notes of a consultant the property of the client?

As a consultant - you were not an employee of the company. Otherwise - the company could have an ownership claim to your notes. Since your consulting contract failed to include materials developed by you which are protected by the US Copyright Laws - you retain ownership of your notes. You should be free to keep them or sell them to the company. Under the Copyright Laws: Copyright protection subsists from the time the work is created in fixed form. (Work = your written notes.) The copyright in the work of authorship immediately becomes the property of the author who created the work. (You are the sole author of your notes.) Only the author or those deriving their rights through the author can rightfully claim copyright. (Absent an agreement regarding your notes - they are yours.)

You need to review your consulting agreement with this client to see if there is any mention of copyright assignment with respect to your notes. Any agreement that you may have signed will be determinative of the outcome here. If client?s counsel did not have you assign patent and copyrights, then the copyright in a work is owned by the work?s creator (you). The client has a legitimate interest in establishing the date of invention for these Patents, so the client may need to negotiate with you to obtain copies of your notes. You may need to retain the assistance of counsel in this matter.

Logically if you don't want to give them over - then don't. See how far they will go. If they file a lawsuit against you then you can decide how much it is worth it to you, to fight the matter. Ostensibly, may i ask -"Do they know what is in your notes and the extent of them?" Do you think they will spend the money to go after you if you don't hand over your notes?

The answer will probably depend on the agreement you signed with the company. If this is a work for hire agreement or you were considered an employee of the company in any way, you may be required to turn over the notes. If there is a challenge to your patents, you may want to voluntarily turn over your notes to protect your IP. In most other situations, a consultant's notes would be his or her private property.

The devil is in the details. It depends on the language of your agreement/contract. For example, you did not say whether the terms provide the company with any ownership or intellectual property rights to your work.