How old should the child be when you tell him/her that he/she is adopted?

From the start, with age appropriate language and books. If you wait until you think they're old enough to understand, they're old enough to feel that everything they understood about the world has suddenly collapsed. Never hide the truth.

Even our 3yr old has a better understanding of the concept than you would think possible.

As soon as possible. I was adopted when I was 3 but never recall not knowing I was adopted. IMO parents should talk about it early so that it's out there even if the child does not fully understand. Nowadays there are Story books about being adopted for very young kids.

From the day that you bring the child home, anything else would be a lie. There should never be a big revelation, the story of how the child came to be in your life should be told, in age appropriate language right from the very start.

The child should always know, if you're not honest right from the start then you are living a lie.

It should never be a Revelation. Start by dripping them age appropriate Information as soon as they Start understanding words.

Old enough to talk.

Don't wait for them to be able to understand it... it should be a part of who they are from the beginning so it doesn't make them question their identity later... They should know they are who they are, and know they are OK... they should not be made to feel that who they are is bad and you needed to hide it from them.

I don't think you should ever hide it because when the kid gets older and funds it he will hold a grudge against you never telling him.

I would be open about it from birth so that it's not a big surprise all of a sudde

its not the time that really matters, its letting them understand, that no matter who their biological parents are, that you were the one that raised them, and that makes you more of a parent than anyone else in the world. you were there all of their life, and you will always be there, and the fact that you love eachother as a family is what really matters. i have relatives that i despise, and i like the guy who gives me my cheese burger at McDonalds more. so find your own words, and try to be prepared for that conversation. as soon as you are, get it out of the way

a teenager would understand the concept of adoption better than a 5 year old.