An isolated antibody or antigen-binding fragment thereof that binds human proprotein convertase subtilisin/kexin type 9 (PCSK9), wherein: (a) the antibody or fragment thereof binds PCSK9 with at least 13 times greater affinity at neutral pH than at acidic pH, as determined by surface plasmon resonance; (b) the acidic/neutral K D ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is greater than about 12.5 as determined by surface plasmon resonance; (c) the acidic/neutral k d ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is greater than about 7.5 as determined by surface plasmon resonance; (d) the acidic/neutral t1⁄2 ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is less than about 0.14 as determined by surface plasmon resonance; (e) the antibody or fragment thereof binds PCSK9 at 25°C and acidic pH with a dissociative half-life (t1⁄2) less than about 4.5 minutes, wherein the antibody or antigen-binding fragment thereof binds PCSK9 at 25°C and neutral pH with a t1⁄2 of greater than about 35 minutes; (f) the antibody or fragment thereof binds PCSK9 with a t1⁄2 at acidic pH that is at least 10 times shorter than the t1⁄2 for the antibody binding to PCSK9 at neutral pH, as measured by surface plasmon resonance; or (g) the antibody or fragment thereof binds PCSK9 with at least 12 times greater affinity at neutral pH than at acidic pH, wherein the antibody or antigen-binding fragment thereof binds PCSK9 with a t1⁄2 at acidic pH that is at least 10 times shorter than the t1⁄2 for the antibody binding to PCKS9 at neutral pH; wherein the antibody or antigen-binding fragment thereof comprises three heavy chain complementarily determining regions (HCDR1, HCDR2 and HCDR3) and three light chain complementarily determining regions (LCDR1, LCDR2 and LCDR3), wherein the HCDR1 comprises SEQ ID NO:220; wherein the HCDR2 comprises SEQ ID NO:222; wherein the HCDR3 comprises SEQ ID NO:224 or 788; wherein the LCDR1 comprises SEQ ID NO:802; wherein the LCDR2 comprises SEQ ID NO:230; and wherein the LCDR3 comprises SEQ ID NO:232. (a) the antibody or fragment thereof binds PCSK9 with at least 13 times greater affinity at neutral pH than at acidic pH, as determined by surface plasmon resonance; (b) the acidic/neutral K D ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is greater than about 12.5 as determined by surface plasmon resonance; (c) the acidic/neutral k d ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is greater than about 7.5 as determined by surface plasmon resonance; (d) the acidic/neutral t1⁄2 ratio for the antibody or antigen-binding fragment binding to PCSK9 at 25°C is less than about 0.14 as determined by surface plasmon resonance; (e) the antibody or fragment thereof binds PCSK9 at 25°C and acidic pH with a dissociative half-life (t1⁄2) less than about 4.5 minutes, wherein the antibody or antigen-binding fragment thereof binds PCSK9 at 25°C and neutral pH with a t1⁄2 of greater than about 35 minutes; (f) the antibody or fragment thereof binds PCSK9 with a t1⁄2 at acidic pH that is at least 10 times shorter than the t1⁄2 for the antibody binding to PCSK9 at neutral pH, as measured by surface plasmon resonance; or (g) the antibody or fragment thereof binds PCSK9 with at least 12 times greater affinity at neutral pH than at acidic pH, wherein the antibody or antigen-binding fragment thereof binds PCSK9 with a t1⁄2 at acidic pH that is at least 10 times shorter than the t1⁄2 for the antibody binding to PCKS9 at neutral pH;