A Skolem sequence of order n is a sequence of 2n integers such that each j = 1,...,n appears exactly twice, separated by exactly j-1 symbols, e.g.,  3453242511 is 
an order 5 Skolem sequence. Such sequences exist iff  n = 0,1 (mod 4),as Th. Skolem showed in 1957. By utilizing the unifying approach of tilings, 
we will survey a number of areas related to Skolem sequences: NP-completeness of the most generalized form of the problem, applications of Skolem sequences and their variants to designs, partitions of arithmetic progressions into arithmetic progressions,
(generating functions are useful here), and two varieties (!) of labelling problems for trees.