What is the top 40 schools in world?

There's no single, universally agreed-upon "top 40" list of universities in the world. Different ranking organizations use different methodologies and weight various factors differently (research output, student/faculty ratio, graduate employability, etc.), leading to different results.

To get an idea of which universities frequently appear at the top, you should consult several reputable ranking systems, such as:

* QS World University Rankings: Focuses heavily on employer reputation and academic peer review.

* Times Higher Education World University Rankings: Considers teaching, research, citations, industry income, and international outlook.

* Academic Ranking of World Universities (ARWU), also known as the Shanghai Ranking: Emphasizes research performance and the number of Nobel laureates and Fields Medalists affiliated with the university.

Each of these ranking systems will produce a different top 40, and the precise schools within that 40 will vary depending on the year. You'll find the most up-to-date rankings on their respective websites. Keep in mind that these rankings should be considered just one factor among many when choosing a university.