We present a theory of quasiperiodic tilings and more general quasiperiodic patterns with long range orientational order. We explain our "strip method" (a variant of the projection methods) on a one dimensional model. Then the icosahedral case is investigated in view of the quasicrystals of the type Al-Mn. Our method allows the study of the local properties (such as the classification of the vertex neighbourhoods) as well as the global ones, and an analytic expression of the Fourier transform is derived, exhibiting the quasiperiodicity.