a b s t r a c tCovering arrays are combinatorial objects that have several practical applications, specially in the design of experiments for software and hardware testing. A covering array of strength t and order v is an N ×k array over Z v with the property that every N ×t subarray covers all members of Z t v at least once. In this work we explore the construction of a Tower of Covering Arrays (TCA) as a way to produce covering arrays that improve or match some current upper bounds. A TCA of height h is a succession of h + 1 covering arrays C 0 , C 1 , . . . , C h in which for i = 1, 2, . . . , h the covering array C i is one unit greater in the number of factors and the strength of the covering array C i−1 ; this way, if the covering array C 0 is of strength t and has k factors then the covering arrays C 1 , . . . , C h are of strength t + 1, . . . , t + h and have k + 1, . . . , k + h factors respectively. We note that the ratio between the number of rows of the last covering array C h in a TCA of height h and the number of rows of the best known covering array for the same values of t, k, and v as for C h is reduced as h grows. Therefore, we search for TCAs with the greatest height possible. The relevant results are the improvement of nineteen current upper bounds for v = 2 and t ∈ {7, 8, 9, 10, 11}, and the construction of twenty-one covering arrays that matched current upper bounds.