\contentsline {section}{\tocsection {}{1}{Introduction}}{2} \contentsline {section}{\tocsection {}{2}{Statement of results and strategy of proof}}{5} \contentsline {subsection}{\tocsubsection {}{2.1}{Stability notions for algebraic curves}}{5} \contentsline {subsection}{\tocsubsection {}{2.2}{Construction of the small contraction $\Psi $}}{7} \contentsline {subsection}{\tocsubsection {}{2.3}{Construction of the flip $\Psi ^+$}}{11} \contentsline {subsection}{\tocsubsection {}{2.4}{Stability results on bicanonical curves}}{12} \contentsline {subsection}{\tocsubsection {}{2.5}{Detailed roadmap for the GIT analysis}}{13} \contentsline {section}{\tocsection {}{3}{GIT of Chow varieties and Hilbert schemes}}{14} \contentsline {subsection}{\tocsubsection {}{3.1}{GIT of Chow points}}{15} \contentsline {subsection}{\tocsubsection {}{3.2}{GIT of Hilbert points}}{16} \contentsline {subsection}{\tocsubsection {}{3.3}{Polarizations on Hilbert schemes}}{17} \contentsline {subsection}{\tocsubsection {}{3.4}{Tautological classes on the Hilbert scheme}}{18} \contentsline {subsection}{\tocsubsection {}{3.5}{Hilbert points and Hilbert schemes}}{19} \contentsline {subsection}{\tocsubsection {}{3.6}{Chow stability and Hilbert stability}}{20} \contentsline {subsection}{\tocsubsection {}{3.7}{Filtered Hilbert polynomials}}{21} \contentsline {subsection}{\tocsubsection {}{3.8}{Hilbert schemes of curves}}{22} \contentsline {section}{\tocsection {}{4}{Basin of attraction and equivalences}}{23} \contentsline {section}{\tocsection {}{5}{Computations over the moduli space of stable curves}}{26} \contentsline {section}{\tocsection {}{6}{Properties of c-semistable and h-semistable curves}}{30} \contentsline {subsection}{\tocsubsection {}{6.1}{Embedding c-semistable curves}}{30} \contentsline {subsection}{\tocsubsection {}{6.2}{Basic properties of tacnodal curves}}{34} \contentsline {section}{\tocsection {}{7}{Unstable bicanonical curves}}{36} \contentsline {subsection}{\tocsubsection {}{7.1}{Badly singular curves are Chow unstable}}{36} \contentsline {subsection}{\tocsubsection {}{7.2}{Polarizations on semistable limits of bicanonical curves}}{38} \contentsline {subsection}{\tocsubsection {}{7.3}{Elliptic subcurves meeting the rest of the curve in one point}}{39} \contentsline {subsection}{\tocsubsection {}{7.4}{Hilbert unstable curves}}{41} \contentsline {section}{\tocsection {}{8}{Classification of curves with automorphisms}}{41} \contentsline {subsection}{\tocsubsection {}{8.1}{Rosaries}}{42} \contentsline {subsection}{\tocsubsection {}{8.2}{Classification of automorphisms}}{44} \contentsline {section}{\tocsection {}{9}{Interpreting the flip via GIT}}{46} \contentsline {section}{\tocsection {}{10}{Stability under one-parameter subgroups}}{49} \contentsline {subsection}{\tocsubsection {}{10.1}{Stability analysis: Open rosaries}}{49} \contentsline {subsection}{\tocsubsection {}{10.2}{Basin of attraction: Open rosaries}}{53} \contentsline {subsection}{\tocsubsection {}{10.3}{Stability analysis: Closed rosaries}}{54} \contentsline {subsection}{\tocsubsection {}{10.4}{Basin of attraction: Closed rosaries}}{57} \contentsline {subsection}{\tocsubsection {}{10.5}{Stability analysis: Closed rosaries with a broken bead}}{57} \contentsline {subsection}{\tocsubsection {}{10.6}{Basin of attraction: Closed rosary with a broken bead}}{60} \contentsline {section}{\tocsection {}{11}{Proofs of semistability and applications}}{61} \contentsline {subsection}{\tocsubsection {}{11.1}{Elliptic bridges and their replacements}}{61} \contentsline {subsection}{\tocsubsection {}{11.2}{Chow semistability of c-semistable curves}}{67} \contentsline {subsection}{\tocsubsection {}{11.3}{ Hilbert semistability of h-semistable curves}}{68} \contentsline {section}{\tocsection {}{}{References}}{73}