Logic Conversion 3.3V to 5V (Current Related) 74HC 74HCT
Whether a 3.3 V signal can reliably drive a 5 V logic input depends on the minimum guaranteed logic high level of the 5 V logic input.  Whether that is sufficiently below 3.3 V for reliable operation varies with logic families and manufacturers, so consulting the datasheet is essential.  For example, Microchip PICs with Schmitt trigger inputs usually require 80% Vdd for guaranteed logic high.  That would be 4.0 V, which is too high to be driven from 3.3 V logic.

A easy hack is to use logic with "T" in its name, like 74HCT as apposed to 74HC.  The T stands for TTL, and means the logic input levels are compatible with the old TTL logic.  This had a finite guaranteed logic high threshold sufficiently below 3.3 V so that driving one of these from 3.3 V logic is fine, although its a good idea to check the specs in any one instant.  So if you need a logic gate in there anyway, make it a HCT type and you get the 3.3 V to 5 V conversion for free.