Counting rational and elliptic curves in CP^2

On a projective plane, two points determine 1 line, five points determine 1 conic, eight points
determine 12 degree three rational curves .... Given 3d-1 points in generic position, how many
degree d rational curves pass through all these points? The numbers in consideration are some
simplest Gromov--Witten invariants. We will review Kontsevich's answer to this question, and
we will review Getzler, Dubrovin--Zhang's answer for genus one.