user11845: I'm still unsure when to use Bitcoin and when bitcoin is more appropriate. Did anyone define when to use the word Bitcoin with a capital B? Is one used to talk about the currency as in "3 Bitcoin" and the other for the "bitcoin protocol"?

user575: Bitcoin (capital B) is the name of a currency, a technology, and a movement. A bitcoin (small b) is a unit of this currency.
Example: "After hearing about Bitcoin, I've installed a Bitcoin client and bought 3 bitcoins."

user11253: From Introduction on the Bitcoin wiki:

Capitalization / Nomenclature
Since Bitcoin is both a currency and a protocol, capitalization can be confusing. Accepted practice is to use Bitcoin (singular with an upper case letter B) to label the protocol, software, and community, and bitcoins (with a lower case b) to label units of the currency.

So, the accepted usage in your example would be "3 bitcoin" and the "Bitcoin protocol".

11845: <p>I'm still unsure when to use <code>Bitcoin</code> and when <code>bitcoin</code> is more appropriate. Did anyone define when to use the word Bitcoin with a capital <code>B</code>? Is one used to talk about the currency as in "3 Bitcoin" and the other for the "bitcoin protocol"?</p>
 575: <p>Bitcoin (capital B) is the name of a currency, a technology, and a movement. A bitcoin (small b) is a unit of this currency.</p>

<p>Example: "After hearing about Bitcoin, I've installed a Bitcoin client and bought 3 bitcoins."</p>
 11253: <p>From <a href="https://en.bitcoin.it/wiki/Introduction" rel="noreferrer">Introduction</a> on the Bitcoin wiki:</p>
<blockquote>
<h1>Capitalization / Nomenclature</h1>
<p>Since Bitcoin is both a currency and a protocol, capitalization can be confusing. Accepted practice is to use Bitcoin (singular with an upper case letter B) to label the protocol, software, and community, and bitcoins (with a lower case b) to label units of the currency.</p>
</blockquote>
<p>So, the accepted usage in your example would be &quot;3 bitcoin&quot; and the &quot;Bitcoin protocol&quot;.</p>
