This paper presents new mechanisms for understanding neutrino masses in superstring models that contain E6-singlet zero mass fields after compactification. The authors show that the low energy gauge group of these models can be phenomenologically acceptable. They also comment on ΔB = 1 and ΔB = 2 baryon number violating processes in these models. The paper discusses the problem of neutrino masses in superstring models, noting that these theories contain both left and right-handed neutrinos, leading to a large Dirac mass for neutrinos. The usual solution to this problem is the "see-saw" mechanism, which generates a large Majorana mass for the right-handed neutrinos. However, in superstring models, the Higgs multiplet that can lead to a large Majorana mass for the right-handed neutrino is absent. As a result, new mechanisms have been considered to solve this problem. The authors propose three categories of mechanisms for generating small neutrino masses: (i) low scale B-L breaking via non-zero v.e.v. for the superpartner of νp; (ii) intermediate scale B-L breaking and use of higher dimensional operators; and (iii) use of E6-singlet Higgs superfields. The paper focuses on the third category and shows that these models can lead to observable neutron-antineutron oscillation while avoiding rapid proton decay. The authors present two models for neutrino masses. In Model I, the authors show that the neutrino is a Dirac particle with a naturally small mass. In Model II, the authors show that the neutrino is a Majorana particle with a small mass. Both models are shown to be consistent with current observations. The authors also discuss baryon number violation in these models. They show that ΔB = 1 transitions are suppressed, while ΔB = 2 transitions may be observable under certain circumstances. The authors also discuss the possibility of neutron-antineutron oscillation in these models. The authors conclude that these models provide a viable framework for understanding small neutrino masses in realistic superstring models. These models avoid catastrophic proton decay and may lead to barely observable neutron-antineutron oscillation under certain circumstances.This paper presents new mechanisms for understanding neutrino masses in superstring models that contain E6-singlet zero mass fields after compactification. The authors show that the low energy gauge group of these models can be phenomenologically acceptable. They also comment on ΔB = 1 and ΔB = 2 baryon number violating processes in these models. The paper discusses the problem of neutrino masses in superstring models, noting that these theories contain both left and right-handed neutrinos, leading to a large Dirac mass for neutrinos. The usual solution to this problem is the "see-saw" mechanism, which generates a large Majorana mass for the right-handed neutrinos. However, in superstring models, the Higgs multiplet that can lead to a large Majorana mass for the right-handed neutrino is absent. As a result, new mechanisms have been considered to solve this problem. The authors propose three categories of mechanisms for generating small neutrino masses: (i) low scale B-L breaking via non-zero v.e.v. for the superpartner of νp; (ii) intermediate scale B-L breaking and use of higher dimensional operators; and (iii) use of E6-singlet Higgs superfields. The paper focuses on the third category and shows that these models can lead to observable neutron-antineutron oscillation while avoiding rapid proton decay. The authors present two models for neutrino masses. In Model I, the authors show that the neutrino is a Dirac particle with a naturally small mass. In Model II, the authors show that the neutrino is a Majorana particle with a small mass. Both models are shown to be consistent with current observations. The authors also discuss baryon number violation in these models. They show that ΔB = 1 transitions are suppressed, while ΔB = 2 transitions may be observable under certain circumstances. The authors also discuss the possibility of neutron-antineutron oscillation in these models. The authors conclude that these models provide a viable framework for understanding small neutrino masses in realistic superstring models. These models avoid catastrophic proton decay and may lead to barely observable neutron-antineutron oscillation under certain circumstances.