This doctoral dissertation is on the theory of Minimal Surfaces and of singularities in Mean Curvature Flow, for smooth submanifolds Y" in an ambient Riemannian (n+ 1)-manifold Nn+1, including: (1) New asymptotically conical self-shrinkers with a symmetry, in R"+1. (1') Classification of complete embedded self-shrinkers with a symmetry, in IR"+1, and of asymptotically conical ends with a symmetry. (2) Construction of complete, embedded self-shrinkers E2 C R3 of genus g, with asymptotically conical infinite ends, via minimal surface gluing. (3) Construction of closed embedded self-shrinkers y2 C R3 with genus g, via minimal surface gluing. In the work there are two central geometric and analytic themes that cut across (1)-(3): The notion of asymptotically conical infinite ends in (1)-(1') and (2), and in (2) and (3) the gluing methods for minimal surfaces which were developed by Nikolaos Kapouleas. For the completion of (2) it was necessary to initiate the development of a stability theory in a setting with unbounded geometry, the manifolds in question having essentially singular (worse than cusp-like) infinities. This was via a Schauder theory in weighted Hölder spaces for the stability operator, which is a Schrodinger operator of Ornstein-Uhlenbeck type, on the self-shrinkers viewed as minimal surfaces. This material is, for the special case of graphs over the plane, included as part of the thesis. The results in (1)-(1') are published as the joint work [KMø 1] with Stephen Kleene, and the result in (2) was proven in collaboration with Kleene-Kapouleas, and appeared in [KKMø 0]. The results in (3) are contained in the preprint [Mø1].

With contributions by leading experts in geometric analysis, this volume is documenting the material presented in the John H. Barrett Memorial Lectures held at the University of Tennessee, Knoxville, on May 29 - June 1, 2018. The central topic of the 2018 lectures was mean curvature flow, and the material in this volume covers all recent developments in this vibrant area that combines partial differential equations with differential geometry.

``Mean curvature flow'' is a term that is used to describe the evolution of a hypersurface whose normal velocity is given by the mean curvature. In the simplest case of a convex closed curve on the plane, the properties of the mean curvature flow are described by Gage-Hamilton's theorem. This theorem states that under the mean curvature flow, the curve collapses to a point, and if the flow is diluted so that the enclosed area equals $\pi$, the curve tends to the unit circle. In thisbook, the author gives a comprehensive account of fundamental results on singularities and the asymptotic behavior of mean curvature flows in higher dimensions. Among other topics, he considers in detail Huisken's theorem (a generalization of Gage-Hamilton's theorem to higher dimension), evolutionof non-convex curves and hypersurfaces, and the classification of singularities of the mean curvature flow. Because of the importance of the mean curvature flow and its numerous applications in differential geometry and partial differential equations, as well as in engineering, chemistry, and biology, this book can be useful to graduate students and researchers working in these areas. The book would also make a nice supplementary text for an advanced course in differential geometry.Prerequisites include basic differential geometry, partial differential equations, and related applications.

In this thesis, we investigate two asymptotic behaviours of the mean curvature flow. The first one is the asymptotic behaviour of singularities of the mean curvature flow, and the asymptotic limit is modelled by the tangent flows. The second one is the asymptotic behaviour of the mean curvature flow as time goes to infinity. We will study several problems related to the asymptotic behaviours. The first problem is the partial regularity of the limit. The partial regularity of mean curvature flow without any curvature assumptions was first studied by Ilmanen. We will follow the idea of Ilmanen to study the partial regularity of other asymptotic limit. In particular, we introduce a generalization of Colding-Minicozzi’s entropy in a closed manifold, which plays a significant role. The second problem is the genericity of the tangent flows of mean curvature flow. The generic mean curvature flow was introduced by Colding-Minicozzi. Furthermore, they introduced mean curvature flow entropy and use it to study the generic tangent flows of mean curvature flow. We study the multiplicity of the generic tangent flow. In particular, we prove that the generic compact tangent flow of mean curvature flow of surfaces has multiplicity 1. This result partially addresses the famous multiplicity 1 conjecture of Ilmanen. One key idea is defining a local version of Colding-Minicozzi’s entropy. We also discuss some related results. These results include a joint work with Zhichao Wang and a joint work with Julius Baldauf.