The overarching goal of this study is to conduct an investigation of regional perspectives on the impact of Israel's nuclear monopoly on nuclear decisions in the Middle East. This Dissertation addresses the question as to why regional actors have taken divergent nuclear paths relative to Israel's nuclear posture. The point of departure for this inquiry is whether the 'introduction' of Israel's nuclear weapons has ever played a pivotal role in the nuclear decisions and escalation dynamics in the Middle East. In so doing, this study addresses why Israel has maintained a nuclear monopoly in the Middle East. Within this context, the nuclear decisions are analyzed while employing three specific Independent Variables, namely: conventional balance; alliance reliance; and the perception of the utility of nuclear weapons. The analysis of the Egypt and Iran cases demonstrated layers of common and divergent responses, namely in relation to their perception of conventional, nonconventional, and nuclear deterrence. The dissertation addressed how both countries perceived and reacted to the underlying principles that underpinned Israel's nuclear posture. The main findings of this dissertation serve the logic of comparison between Egypt and Iran. These findings are addressed in terms of: a) the essence of reaction whether it applies to the nuclear posture or nuclear capabilities; b) the mere existence of a nuclear decision; c) the perception of the utility of nuclear weapons in terms of deterrence, compellence, and coercion; d) the difference between the official, semi-official and unofficial rhetoric; e) the significance of the legal reaction. / Doctor of Philosophy / This dissertation addressed two comparative reactions to Israel's nuclear posture, namely Egypt's and Iran's divergent nuclear paths. In so doing, it addressed the nuclear decisions of Egypt and Iran from 1955 to 2021. This dissertation made an effort in investigating how a tacit ally, namely the Shah, perceived Israel's nuclear posture. As analyzed, the literature tends to overlook the story of Iran's reaction under the Shah. Therefore, more research is necessary to decipher the puzzle of why allies feel alarmed or concerned by a nuclear ambition of a close regional partner. An important issue that this dissertation addressed while investigating reactions to Israel's nuclear posture was the delicate issue of decoupling Israel's posture from other established nuclear powers or nuclear aspirants. Within this context, it is central that this study underscores the impacts of the Indian, and Pakistani bombs and the impact of Iraq's nuclear ambition and to make a strong and substantiated case as to why Iran's reaction addressed Israel's posture and not Iraq or India. The same analysis applies to Egypt which witnessed the emergence of another nuclear aspirant in the 1980s, namely Iraq. In the final analysis, the main findings of this dissertation support the argument that comparative regional reactions to Israel's nuclear posture help investigate and test the main assumptions that underpinned opacity. Within this context, future researchers might further analyze the trichotomy of conventional; nonconventional, and nuclear deterrence because regional actors might employ the case of monopoly for explicit or tacit bargaining that fulfills the overarching interest of guaranteeing a robust conventional force. The underlying foundation of this research is to address how regional actors perceive and react to asymmetries in power, resolve, and stake.