This paper is a discussion of Hegel's conception of the principle 'omnis determinatio est negatio', which he attributes to Spinoza. It is argued, however, that Spinoza understood this principle in a very different way from Hegel, which then sets up an interpretative puzzle: if this is so, why did he credit Spinoza with formulating it? This puzzle is resolved by paying attention to the context in which those attributions are made, while it is also shown that the British Idealists (unlike many contemporary commentators) were aware of the complexities in the Spinoza-Hegel relation on this issue. The paper also addresses some of the philosophical debates raised by this question, and the light it sheds on Hegel's critique of Spinoza as a monist.This paper concerns an interpretative puzzle, and also the philosophical lessons that can be learnt from it. The interpretative puzzle concerns Hegel's use of the slogan 'all determination is negation', where this idea forms an important part of Hegel's metaphysical thinking, and one that he is often said to have got from Spinoza, based not least on comments Hegel himself makes. But in fact, the way in which Hegel understands the doctrine seems to be the opposite of the way in which Spinoza understood it: roughly, for Hegel the negation that comes with determination is necessary for being in any genuine sense, whereas for Spinoza the negation that comes with determination is a privation of being, a way of not being -so while for Hegel such determination through negation is a necessary condition if being is not to collapse into nothing, for Spinoza it is a taking away of being. How, then, did this inversion come about; why didn't Hegel make it clearer; and why has it been so frequently missed? And, philosophically speaking, what hangs on it, and what role does it play in Hegel's critique of Spinoza?In this paper, I want to examine what this difference between the Hegelian and Spinozistic ways of taking the doctrine amounts to, and how it is to be explained. I also want to explore the impact this difference had on the British Idealists. I will argue that several of the British Idealists (unlike several contemporary Hegel commentators) clearly saw the contrast between Spinoza and Hegel here, where some