Since I had conscious thoughts I have never believed. I remember being around 3 years old and wondering what the weird adults were doing when they were praying. Praying above all gave me the heebie-jeebies. Not only did I find the whispered words and the emotional pained faces creepy, but I wanted to know who they were appealing to, as it was clear to me they were appealing to a nothingness. When I was 7 I learned about the holocaust. When I saw the bodies, and also learned of great heroics, I knew for a fact that ‘evil’ was a manifestation of our worst nature and “good” was a manifestation of our best nature. God and the Devil are excuses for not doing the right thing, and prayer is pretending to do something. It’s nonsense. So, I guess I was born a logical humanist.

For me, it was a long, drawn out process. I was raised evangelical christian and had religion shoved down my throat. Then in subsequent years I spent a lot of time bouncing around and studying various religions. I really got to a point where I felt that religion was really about control and fear. Also, I really demanded proof for the things around me. I'm naturally a skeptic and if things can't be quantified with facts I tend to have precious little patience.

None... I was born without a god. So catholic school made no difference. No research, no book, no teaching, no internet, no hero, no information, NOTHING.

There was one trigger moment that did it: one moment that started me on the path to rationalism.

As a child, I started as a naive atheist. My parents took me to Sunday school, and I'd hear all of these ridiculous stories, and I let my opinions be known.

"Jesus is sitting next to you, and he's crying," my Sunday school teacher said.

"There's no one there."

"I can see him, and he's crying," she replied.

OK, these people had some serious delusions.

The second step was when I bought a copy of James Randi's book "Flim Flam!" That was the missing part! Before, I was an atheist because I thought religious ideas were idiotic. I still harbored belief in UFOs, ESP, and so on.

Then, I realized that a fat better argument was that there is no evidence for a God.

And then I went to the task of going over what I believed, and seeing if those beliefs had any evidence to back them up.

But here's an interesting thing: many times my first reaction to something will be decidedly irrational. And then I'll ask myself what evidence I have. That is a tremendous help, especially in interpersonal relationships.

It was a lack of information.

Poor and weak evidence for the god claim. Improbability. Seemingly man written holy books with so many flaws that disqualify it from being inspired by a perfect being. Holy books with claims about the universe that aren't possible such as plant life happening before the creation of the sun. I tend to follow "what can be asserted without evidence can be dismissed without evidence." (Hitchens Razor)
Person A: Invisible Unicorns exist!
Person B: Oh really, can you prove it?
Person A: You can't prove that they don't, you have to have faith in them.
Person B: Invisible fairists, cyclopists, minotaurists, and leprachaunists also have faith, anything imaginable no matter how ridiculous can be asserted on faith, I have no reason to think yours is any different nor do I have any reason in disproving something being asserted without substantial or good evidence. I do not believe you, I'm an a-invisible unicornist.
I'm person B. I'd like to add that we used to think many things were magical until science gave a much better and evidenced explaination. Just because there are gaps in science doesn't mean folks can insert god to fill in the gap without any evidence--but you can can say you don't know. I don't know whether or not a god or god(s) exists but have seen no good reason to say that they do so I live my life as if they don't exist and I'm doing fine. I do think a non-intervening god is much more possible than one like the god of abraham but do not believe it either because I have no reason to unless it can be back up with evidence. I'm both agnostic (open to the possibility of there being god(s) and not 100% certain of nonexistence) and atheist (I do not believe in god(s) because they fail to meet their burden of proof). I also see no point in believing things just because I find them personally appealing, I care about truth, not comfort.

The Bible. It was very contradictary.

Also lack of proof. Period.

Critically examining the claims of my faith. I was motivated to do that by my faith not accurately explaining or predicting experienced reality, which is a pretty good sign that your epistemology (means of determining what is true) sucks.

Lack of information for anything else.

The whole Christian thing never made sense and the more I looked into it the less it made. It just never stood up under any scrutiny.

Common sense I guess. I grew up in church. I always knew it was rediculous. I got kicked out of Sunday school more than once for asking questions like if Adam and Eve had Cain and Abel and Cain killed Abel how the hell did Cain go get married? If they couldn't answer my question they just said I was full of the devil and I need to leave. Bahaha

12 years of Catholic Education did it for me LOL

None, I never was a, Theist. Didnt grow up in any religion and have never wanted or needed one,
It doesnt bother me at all to walk into a church to have a look, there is a lovely little place in Eyam that was the plague village - In 1665 a wandering journeyman was carrying bolts of cloth from London to Derbyshire during the bubonic plague and the fleas were in the roll of material. he stopped at Eyam and the village decided once the plague had taken hold there -to just contain it They had a large stone at the village boundary with a dip in it they filled with vinegar so that they could buy stuff without spreading the plague. 260 out of 350 inhabitants died but their voluntary sacrifice saved the North of England from succumbing. It is kept just as it was and htere are plaques on the houses with the names of who died there.

My deconversion started when I read the bible for a class in college. The contradictions made me think and loss of belief followed quickly! Nothing in the following 40 years has changed my opinion.

It's not a matter of evidence leading me to atheism but rather a lack of evidence allowing me to remain an atheist.

Reaching the age of reason.

Science, specifically the scientific method. If it isn't falsifiable, it isn't real.

As others have said, I read the Bible when I was a Presbyterian. I am a voracious reader and my dad bet me I couldn't read the bible. Well, the result wasn't what he expected. I also realized that, after readign many other mythos, they were basically the same, and prayers to no god worked.

A serious reading of the Bible with the intent of really understanding it. I was not seeking trouble, I was trying to be a better Christian.

Going to seminary.

I became fascinated when studying history, and noted that it certainly didnt' line up with what the religious texts were saying. Then I studied the history behind the texts themselves, and never looked back.

One day, in 5th grade, I suddenly realized I didn't believe in God

Religion was never big in our family, but when my oldest brother turned born again christian and pushed his views down our throats, it was then I started to really question what I believed, and through trial and tribulation, and frankly common sense, I decided to consider being atheist. It was ultimately the documentary "Unbelievers" that made me certain.

I read somewhere that atheists have different brain patterns to believers. Perhaps we are wired that way.