Variable names Local variables, method paramaters and method names: start with a lower case letter and don’t follow the camel case convention instead, eg. my_var, my_method_name(withMyParameter). Also method names can end in ?,! and = Global variables start with a $, eg. $my_global_variable Instance variables start with an @, eg. @instance_variable. Whereas previous variables “could” follow camel case convention, instance variables do not. So you would not see @instanceVariable. Class variables start with a @@, eg. @@my_class_variable With regards to @ and @@, normally pretty much any character can follow @, with the exception of digits. Class names, module names and constants should start with an upper case letter, eg. MySuperDuperClassName (I prefer constants to be all UPPER CASE) Arrays and Hashes Arrays are accessed by a numeric key (and use […]), hashes support an object as accessor as well (and use {…}). They grow dynamically. Array elements are more efficient, but hashes are more flexible. To access a hash index you still use [], eg. hash[key] Accessing a hash by a missing key (or you can say indexed by a missing key) returns nil.