It is very important that you try to keep your invention confidential until you have your first patent application (likely a US provisional patent) on file. Ultimately, disclosure of the invention to the public will always end your ability to file a patent – the only question being whether this deadline falls before or after you have actually filed. The answer may vary from country to country.
Most countries in the world (eg. Europe, China, etc.) have an ‘absolute novelty’ patent regime. This means that if the invention has been “disclosed” by anyone anywhere before you file your patent application you cannot patent that invention. Thus, if you disclose before filing the patent application, you will be barred from patenting in all absolute novelty jurisdictions (and of course, it is never possible to patent an invention that someone else has disclosed before you either filed or disclosed).
Canada and the United States have a limited exception to the ‘absolute novelty’ rule. They permit you to file a patent application up to 12 months after you first disclosed the invention, provided your disclosure must be before any other disclosure or patent filing by anyone else (ie. you must still have been the first inventor to disclose or patent the invention). Some other countries have limited grace periods (eg. 6 months in Japan for certain limited disclosures).
The mirror image of keeping an invention confidential is ‘disclosing’ it to the public. The precise definition of “disclosure to the public” differs from country to country. Of course, disclosure of the invention in private to individuals who owe you a duty of confidence (see below) is not a “disabling disclosure” (ie. a disclosure that will bar patenting – either now in absolute novelty jurisdictions or after the 12-month grace period in Canada and the US) can be any form anywhere in the world (eg. a simple web page will suffice) but must be “enabling”. This means that a person of ordinary skill in the art must have been able to determine your invention from the disclosure that you made. In the United States, disabling disclosure does not need to be ‘enabling’. Printed publications are disabling disclosures, and offering to sell any product (or service) that embodies the invention is disabling disclosure in the United States (known as the “on-sale bar”). Canada does not have an on-sale bar per se.
A disclosure of your invention to an individual who owes you a duty of confidence is not a public disclosure that will prevent you from patenting the invention. Duties of confidence may arise contractually (as from a signed ‘Confidentiality Agreement’, or ‘Non-disclosure Agreement (commonly called an NDA)), by implication, or from the implied terms of a type of relationship. For instance, patent agents and lawyers always owe their clients fiduciary obligations of confidentiality and non-competition (and in the case of lawyers, all communications with them are privileged).
The fiduciary obligations owed by patent agents and lawyers to their clients to retain invention disclosures in strict confidence last indefinitely, and are generally much stronger, and broader, than most contractual duties of confidence. As a result, you should be able to freely disclose your invention to your patent agent and patent lawyer without requiring an NDA. As a general rule patent agents and lawyers also owe their clients a duty to avoid all manner of conflicts of interest; certainly, this extends to not competing commercially with their clients during the term of their engagement and for some period thereafter. In our case, we always try to avoid acting for clients who might have any competing patent or trademark interests.