In this lecture we are concerned with the following biharmonic equation Δ2u(x)=uq(x) x ∈Ω, u(x)=Δu(x)=0 x ∈∂Ω (P$ε$) where q=ε+(n+4)/(n−4), Ω is a smooth bounded domain in Rn (n≥5), and ε is a real number. We study the asymptotic behaviour of solution of (P$ε$) which are minimizing for the Sobolev quotient as ε is negative and goes to zero. We show that such solutions concentrate around a point p∈Ω, moreover p is a critical point of the Robin’s function. Conversely, we show that for any nondegenerate critical point p of the Robin’s function there exists solutions of (P$ε$) concentrating around p. Finally we prove that, in contrast with what happened in the above case, the supercritical problem (that is (P$ε$) with ε>0) has no solutions which concentrate around a point of Ω.