The paper updates constraints on the fraction of the universe that could have been primordial black holes (PBHs) with masses in the range 10^9–10^11 g, focusing on the effects of their evaporations on big bang nucleosynthesis (BBN) and the extragalactic photon background (EGB). It includes for the first time the effects of quark and gluon emission by black holes and accounts for recent observational developments. The constraints derived from BBN and EGB are found to be the dominant ones over the mass range 10^9–10^17 g. The paper also discusses other constraints in this mass range and shows that they are weaker than the BBN and EGB limits, except for a small range 10^13–10^14 g where the damping of cosmic microwave background anisotropies dominates. Additionally, the paper reviews the gravitational and astrophysical effects of non-evaporating PBHs over a broader mass range of 1–10^50 g. The constraints on the fraction of the universe that could have been PBHs are updated, and the implications for cosmological models are discussed.The paper updates constraints on the fraction of the universe that could have been primordial black holes (PBHs) with masses in the range 10^9–10^11 g, focusing on the effects of their evaporations on big bang nucleosynthesis (BBN) and the extragalactic photon background (EGB). It includes for the first time the effects of quark and gluon emission by black holes and accounts for recent observational developments. The constraints derived from BBN and EGB are found to be the dominant ones over the mass range 10^9–10^17 g. The paper also discusses other constraints in this mass range and shows that they are weaker than the BBN and EGB limits, except for a small range 10^13–10^14 g where the damping of cosmic microwave background anisotropies dominates. Additionally, the paper reviews the gravitational and astrophysical effects of non-evaporating PBHs over a broader mass range of 1–10^50 g. The constraints on the fraction of the universe that could have been PBHs are updated, and the implications for cosmological models are discussed.