Base64 (MIME) Encode and Decode Tool is a tool to turn binary data into text (encode) or text into binary (decode). To allow binary data to be transmitted with textual data it must be encoded. An example of this is an attachment in an email. This is done via the MIME implementation of Base64. The MIME implementation uses the characters A-Z, a-z, and 0-9 for the initial 62 values that it can use to encode data.
The term Base 64 is generic, and there are many implementations. MIME, which stands for Multi-Purpose Internet Mail Extensions, is the most common that is seen today. It is used to transmit attachments via email over the Simple Mail Transfer Protocol (SMTP). Other examples of Base64 encoding are Radix-64 and YUI's Y64. Encoding data in Base64 results in it taking up roughly 33% more space than the original data.
You should use Base64 whenever you intend to transmit binary data in a textual format.