G = General Audiences = All ages can read.
PG = Parental Guidance suggested = All ages can read with adult supervision.
PG-13 = Parental Guidance under 13 = 13 yr olds and older can read.
R = Restricted = Only adults can read. May contain curse words or violent situations.
NC-17 = No children under 17 = Contains adult situations and sexually explicit scenes. NOT for minors.