Let B be an infinite subset of {1, 2, . . . }. We characterize arithmetic and dynamical properties of the B-free set F B through group theoretical, topological and measure theoretic properties of a set W (called the window) associated with B. This point of view stems from the interpretation of the set F B as a weak model set. Our main results are: B is taut if and only if the window is Haar regular; the dynamical system associated to F B is a Toeplitz system if and only if the window is topologically regular; the dynamical system associated to F B is proximal if and only if the window has empty interior; and the dynamical system associated to F B has the "naïvely expected" maximal equicontinuous factor if and only if the interior of the window is aperiodic.Therefore the implication (i) ⇒ (iii) of Theorem A is an immediate consequence of the following proposition. Proposition 1.1. Assume that B is taut. Let h ∈ W and S ⊂ B finite. Then the set of B-free integers n that solve n = h b mod b for b ∈ S has asymptotic density m H (U S (h) ∩ W) > 0.In Subsection 2.4 we provide a sequence B, which is not taut, but for which ∆( ) ∩ W = W (Example 2.2). Hence (iii) of Theorem A is not equivalent to (i) and (ii). Here we provide two simpler examples which throw some light on property (iii). Denote by P ⊆ AE the set of all prime numbers. Example 1.1. If B = P then H = p∈P /p , W is uncountable (although of Haar measure zero) and ∆( ) ∩ W W, since for each n we find p ∈ P such that p | n, so n = 0 mod p. Example 1.2. If B ⊂ P is thin, i.e. if p∈B 1/p < +∞, then ∆( ) ∩ W = W in view of (4), because each h ∈ H satisfies the B-free CRT. Indeed, if S ⊂ B is finite and n = h b mod b for b ∈ S , then n + lcm(S ) is the set of all solutions to this system of congruences. Moreover, if h ∈ W, then gcd(n, b) = 1 for all b ∈ S . We only need to find r ∈ so that n + r lcm(S ) is a prime number which is not in B. The latter follows from Dirichlet's theorem: The set of prime numbers contained in n + lcm(S ) is not thin. Of course this is a special case of Theorem A. Remark 1.2. Denote by ν η := m H • ϕ −1 the Mirsky measure on X η . There are two independent proofs of the fact that the two equivalent conditions from Theorem A imply that the measure preserving dynamical system (X η , σ, ν η ) is isomorphic to the group rotation (H, R ∆(1) , m H ): In [4, Theorem F] it is proved that this is implied by (i). That it is also a direct consequence of (ii) follows -in the more