Consider the first-order linear differential equation with several retarded arguments x ′ (t)+ ∑ i = 1 m p i (t)x ( τ i ( t ) ) =0,t≥ t 0 , where the functions p i , τ i ∈C([ t 0 , ∞), R + ) for every i=1,2,…,m, τ i (t)≤t for t≥ t 0 and lim t → ∞ τ i (t)=∞. A survey on the oscillation of all solutions to this equation is presented in the case of several non-monotone arguments and especially when well-known oscillation conditions are not satisfied. Examples illustrating the results are given.MSC:34K11, 34K06.