We recall Lennart Carleson's Theorem asserting the pointwise 
convergence of partial summation of Fourier series.  We 
explain what the Theorem says, and why it is difficult.  
We explain why the Theorem is worty of citation by the Abel 
Prize committee:  It is a "multi-scale" theorem.  The talk 
finishes with results that are related, as well as new 
results of Victor Lie and also Xiaochun Li that point to 
certain non-commutative developments.