Can you copyright an idea?

No. 17 USC 102(b) excludes ideas, procedures, processes, systems, methods of operation, concepts, principles and discoveries — expressly regardless of how they are described or illustrated. Writing the idea down in detail protects the document, not the idea. Someone may read it, take the concept and build it without infringing.

How do I protect an idea before pitching it?

An NDA is the only instrument that gives you a claim against that particular party, and it works because they agreed rather than because you own anything. Keep the idea a trade secret until then, disclose the minimum needed, and keep dated records of what you disclosed and when. Many investors will decline to sign, which is a real constraint.

Does mailing myself a description of my idea protect it?

No, on two counts. There is no right in an idea for it to create, and as evidence a sealed envelope is weak — the trick of posting an unsealed envelope and filling it later is well known, and courts have rejected the practice repeatedly. It is not a substitute for registration, a contract or secrecy.

Is a patent the answer?

Only if you have a specific, novel, non-obvious invention rather than a general concept, and only if you can bear the cost and delay. A patent also requires publishing the invention, which ends any trade secret protection permanently. For many software and business ideas it is neither available nor economic.

Trademark vs Copyright for an Idea

Key takeaways

Copyright protects expression, never ideas. 17 USC 102(b) says so explicitly.
Trademark protects names and brands, not concepts.
A patent can protect an invention, which is a specific implementation, not a general idea.
Contracts and secrecy are the only tools that give you leverage over an idea as such.

The short answer

You cannot own an idea. You can own a particular expression of it, a name for it, an implementation of it, or a promise from someone not to use it.

Why copyright cannot help

17 USC 102(b) is unusually blunt:

In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work.

Note the last clause. Writing your idea down in great detail does not bring it inside copyright. The document is protected; the idea in it is not. Someone can read your description, take the concept, and build it, without touching your copyright.

This is deliberate. Copyright in ideas would make it impossible to write, build or think in the vicinity of anyone else's work.

Why trademark cannot help

Trademark protects signs that identify commercial source. It has nothing to say about concepts. You can trademark what you call your idea once you are selling something under that name — which protects the brand, not the idea.

What "poor man's copyright" is not

Mailing yourself a sealed envelope does not create a right in an idea, because no right in an idea exists to create. It also does not do the smaller thing people hope for: an envelope is easy to fake — post an unsealed one and fill it later — and it has been rejected repeatedly. See poor man's copyright and the alternative.

What actually works

A contract. An NDA is the only instrument that gives you a claim against a specific person for using your idea. It works because they agreed, not because you own anything. It requires a counterparty with a reason to sign — which is why NDAs work with employees, contractors and serious commercial partners, and why most investors decline.

Trade secret. If the idea has commercial value from not being known, and you take reasonable steps to keep it secret, trade secret law gives you a remedy against misappropriation. It ends the moment you publish.

A patent. Not for the idea, but for a specific novel and non-obvious invention that implements it. Expensive, slow, and it requires publishing the invention in exchange for the monopoly.

Execution. Unsatisfying, and usually the real answer. Ideas are widely distributed; the scarce thing is building the thing.

Side by side

	Protects an idea?	What it does protect
Copyright	No	Your specific written or visual expression
Trademark	No	The name you sell it under
Patent	Partly	A specific novel implementation
Trade secret	Yes, while secret	Confidential commercially valuable information
NDA	Yes, against that party	Whatever the contract says
Poor man's copyright	No	Nothing

Where a timestamp fits, honestly

A timestamp does not protect an idea. Nothing does, absent a contract or secrecy.

What it does is create a dated, tamper-evident record that a document existed on a date. That is useful in three narrow situations:

Before an NDA-covered disclosure, to fix exactly what you disclosed and when — which matters if the agreement is later disputed.
As part of a trade secret file, evidencing that you held specific confidential information at a specific time without publishing it.
As inventorship evidence, where a dated record of conception supports a patent position.

In all three the timestamp is supporting evidence around a right created by something else. Anyone selling you a timestamp as protection for an idea is selling you something that does not exist. See proof of existence vs proof of authorship and how to protect an idea.

US law. This is general information, not legal advice.

Trademark vs copyright for an idea