The main aim of this thesis is divided into two parts. The first part is devoted to the study of the problem,\begin{equation} \label{Equ.1.resume.anglais}\left\{\begin{aligned}-\Delta u \, + u &= 0 ~~ \text{in} ~~ \Omega, \\ \frac{\partial u}{\partial n} \,+ \, g(u) &= \mu ~~ \text{on} ~~ \partial \Omega,\end{aligned}\right .\end{equation}where Ω is a bounded regular domain of RN, g(⋅) is a continuous function that satisfies the sign condition s⋅g(s)≥0, in some model case we will assume that g(⋅) is increassing, and finally μ is a bounded measure on ∂Ω. Some of our results remain true when Ω:=R+N.We will start by proving the existence of a solution when μ is an L1(∂Ω) function, and this independently of the nonlinearity g(⋅) that satisfies the previous hypothesis. Then, we will study the case when μ is a Radon measure on ∂Ω. In such a context, some new conditions appear on g(⋅) and μ that assure the existence of a solution. We will prove the existence of a solution when g(⋅) is a sub-critical nonlinearity in dimension N larger or equal to three, and when g satisfies the weak singularity assumption on the boundary in case N equals two. When Ω:=R+2 and μ:=cδ0, our result states that the problem admits a solution if and only if a−(g)π≤c≤a+(g)π,where a−(g) and a+(g) denote the exponential order of growth of the function g(⋅), respectively at minus and plus infinity.Finally, we fix g(u):=∣u∣p−1u, where p>1, so we will prove that the problem admits a solution if the measure μ is diffuse with respect to the capacity C1,p′. After, if μ is a positive measure for which this problem admits a solution, then necessarily this measure must be diffuse with respect to the capacity C1,p′. This allows us to deduce that if c∈R∗ and a∈∂Ω, then the problem with data μ=cδ0 does not have a solution whenp≥N−2N−1. The second part of this thesis is devoted to study the singularities of the problem, \begin{equation}\label{Equ.2.resume.ang} \left\{\begin{aligned}&- \Delta u = 0 ~~ \text{in} ~~ \Omega, \\ &\frac{\partial u}{\partial n} \,+ \, |u|^{p-1}\, u = 0 ~~ \text{on} ~~ \partial \Omega \backslash \{a\},\end{aligned}\right .\end{equation}where Ω is a bounded regular domain of RN such that a∈∂Ω, p>1 and the function u is smooth enough in Ω∖{a}. Without loss of generality we fix a to be the origin 0.We will see that the nature of the singularity depends on the critical parameter pc:=N−2N−1.We will prove that the singularity is removable in the case p≥pc. In the second case when 11, alors on montrera que le problème admet une solution si la mesure μ est absolument continue par rapport à la capacité C1,p′. Puis, dans le cas où le problème admet une solution pour une mesure de Radon positive μ, alors nécessairement cette mesure est absolument continue par rapport à la capacité C1,p′. Ceci permet de déduire que si c∈R∗ et a∈∂Ω alors le problème à donnée μ=cδa n'admet pas de solution lorsque : p≥N−2N−1. La deuxième partie de cette thèse est consacrée à l'étude de singularités du problème,\begin{equation}\label{Equ.2.resume} \left\{\begin{aligned}&- \Delta u = 0 ~~ \text{dans} ~~ \Omega, \\ &\frac{\partial u}{\partial n} \,+ \, |u|^{p-1}\, u = 0 ~~ \text{sur} ~~ \partial \Omega \backslash \{a\},\end{aligned}\right .\end{equation}où Ω est un ouvert régulier borné de RN tel que a∈∂Ω, p>1 et la fonction u est suffisamment régulière dans Ω∖{a}. Sans perte de généralité on fixe a comme étant l'origine 0.On verra que la nature de singularité dépend du paramètre critique : pc:=N−2N−1. On montrera que la singularité est éliminable lorsque p≥pc. Lorsque 1<p<pc, en considérant les coordonnées sphériques, on obtiendra que rp−11u(r,σ) converge quand r→0 vers une composante compacte et connexe d'un certain ensemble E. Maintenant, si 1/(p−1)∈/N, et si l'une de conditions suivantes a lieu :i) si N=2, ii) si u(x)∣x∣p−11→0, quand ∣x∣→0, iii)si u est positive et (N−1)N<p<pc,alors, on déduit une classification précise des singularités de l'équation. Ces résultats seront énoncer respectivement dans Théorème 4.13, Théorème 4.12 et Théorème 4.11