Summary: We study sequential dynamical systems (SDS) over words. Our main result is the classification of SDS over words for a fixed graph \(Y\) and a family of local maps \((F_{v_i})\) by means of a novel notion of SDS equivalence. This equivalence arises from a natural group action on acyclic orientations. An SDS consists of: (a) a graph \(Y\), (b) a family of vertex indexed \(Y\)-local maps \(F_{v_i}:K^n\to K^n\), where \(K\) is a finite field and (c) a word \(w\), i.e. a family \((w_1,\dots,w_k)\), where \(w_j\) is a \(Y\)-vertex. A map \(F_{v_i}(x_{v_1},\dots, x_{v_n})\) is called \(Y\)-local iff it fixes all variables \(x_{v_j}\neq x_{v_i}\) and depends exclusively on the variables \(x_{v_j}\), for \(v_j\in B_1(v_i)\). The SDS-map is obtained by composing the local maps \(F_{v_i}\) according to the word \(w: [(F_{v_i})_{v_i\in Y},w]= \prod_{i=1}^k F_{w_i}:K^n\to K^n\). Mutual dependencies of the local maps arising from their sequential application are expressed in the graph \(G(w,Y)\) having the vertex set \(\{1,\dots,k\}\) (the indices of the word \(w\)) and in which \(r,s\) are adjacent iff \(w_s,w_r\) are adjacent in \(Y\). We prove a bijection from equivalence classes of SDS-words into equivalence classes of acyclic orientations of \(G(w,Y)\). We show that within these equivalence classes the induced SDS are equivalent in the sense that their respective phase spaces are isomorphic as digraphs.