diff --git a/src/strconv/atoc.go b/src/strconv/atoc.go
new file mode 100644
index 00000000000000..55b7c23ee7aa50
--- /dev/null
+++ b/src/strconv/atoc.go
@@ -0,0 +1,105 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv
+
+const fnParseComplex = "ParseComplex"
+
+// convErr splits an error returned by parseFloatPrefix
+// into a syntax or range error for ParseComplex.
+func convErr(err error, s string) (syntax, range_ error) {
+	if x, ok := err.(*NumError); ok {
+		x.Func = fnParseComplex
+		x.Num = s
+		if x.Err == ErrRange {
+			return nil, x
+		}
+	}
+	return err, nil
+}
+
+// ParseComplex converts the string s to a complex number
+// with the precision specified by bitSize: 64 for complex64, or 128 for complex128.
+// When bitSize=64, the result still has type complex128, but it will be
+// convertible to complex64 without changing its value.
+//
+// The number represented by s must be of the form N, Ni, or N±Ni, where N stands
+// for a floating-point number as recognized by ParseFloat, and i is the imaginary
+// component. If the second N is unsigned, a + sign is required between the two components
+// as indicated by the ±. If the second N is NaN, only a + sign is accepted.
+// The form may be parenthesized and cannot contain any spaces.
+// The resulting complex number consists of the two components converted by ParseFloat.
+//
+// The errors that ParseComplex returns have concrete type *NumError
+// and include err.Num = s.
+//
+// If s is not syntactically well-formed, ParseComplex returns err.Err = ErrSyntax.
+//
+// If s is syntactically well-formed but either component is more than 1/2 ULP
+// away from the largest floating point number of the given component's size,
+// ParseComplex returns err.Err = ErrRange and c = ±Inf for the respective component.
+func ParseComplex(s string, bitSize int) (complex128, error) {
+	size := 128
+	if bitSize == 64 {
+		size = 32 // complex64 uses float32 parts
+	}
+
+	orig := s
+
+	// Remove parentheses, if any.
+	if len(s) >= 2 && s[0] == '(' && s[len(s)-1] == ')' {
+		s = s[1 : len(s)-1]
+	}
+
+	var pending error // pending range error, or nil
+
+	// Read real part (possibly imaginary part if followed by 'i').
+	re, n, err := parseFloatPrefix(s, size)
+	if err != nil {
+		err, pending = convErr(err, orig)
+		if err != nil {
+			return 0, err
+		}
+	}
+	s = s[n:]
+
+	// If we have nothing left, we're done.
+	if len(s) == 0 {
+		return complex(re, 0), pending
+	}
+
+	// Otherwise, look at the next character.
+	switch s[0] {
+	case '+':
+		// Consume the '+' to avoid an error if we have "+NaNi", but
+		// do this only if we don't have a "++" (don't hide that error).
+		if len(s) > 1 && s[1] != '+' {
+			s = s[1:]
+		}
+	case '-':
+		// ok
+	case 'i':
+		// If 'i' is the last character, we only have an imaginary part.
+		if len(s) == 1 {
+			return complex(0, re), pending
+		}
+		fallthrough
+	default:
+		return 0, syntaxError(fnParseComplex, orig)
+	}
+
+	// Read imaginary part.
+	im, n, err := parseFloatPrefix(s, size)
+	if err != nil {
+		err, pending = convErr(err, orig)
+		if err != nil {
+			return 0, err
+		}
+	}
+	s = s[n:]
+	if s != "i" {
+		return 0, syntaxError(fnParseComplex, orig)
+	}
+	return complex(re, im), pending
+}
diff --git a/src/strconv/atoc_test.go b/src/strconv/atoc_test.go
new file mode 100644
index 00000000000000..5c817a2e44b6f5
--- /dev/null
+++ b/src/strconv/atoc_test.go
@@ -0,0 +1,195 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv_test
+
+import (
+	"math"
+	"math/cmplx"
+	"reflect"
+	. "strconv"
+	"testing"
+)
+
+var (
+	infp0 = complex(math.Inf(+1), 0)
+	infm0 = complex(math.Inf(-1), 0)
+	inf0p = complex(0, math.Inf(+1))
+	inf0m = complex(0, math.Inf(-1))
+	infpp = complex(math.Inf(+1), math.Inf(+1))
+	infpm = complex(math.Inf(+1), math.Inf(-1))
+	infmp = complex(math.Inf(-1), math.Inf(+1))
+	infmm = complex(math.Inf(-1), math.Inf(-1))
+)
+
+type atocTest struct {
+	in  string
+	out complex128
+	err error
+}
+
+func TestParseComplex(t *testing.T) {
+
+	tests := []atocTest{
+		// Clearly invalid
+		{"", 0, ErrSyntax},
+		{" ", 0, ErrSyntax},
+		{"(", 0, ErrSyntax},
+		{")", 0, ErrSyntax},
+		{"i", 0, ErrSyntax},
+		{"+i", 0, ErrSyntax},
+		{"-i", 0, ErrSyntax},
+		{"1I", 0, ErrSyntax},
+		{"10  + 5i", 0, ErrSyntax},
+		{"3+", 0, ErrSyntax},
+		{"3+5", 0, ErrSyntax},
+		{"3+5+5i", 0, ErrSyntax},
+		// Parentheses
+		{"()", 0, ErrSyntax},
+		{"(i)", 0, ErrSyntax},
+		{"(0)", 0, nil},
+		{"(1i)", 1i, nil},
+		{"(3.0+5.5i)", 3.0 + 5.5i, nil},
+		{"(1)+1i", 0, ErrSyntax},
+		{"(3.0+5.5i", 0, ErrSyntax},
+		{"3.0+5.5i)", 0, ErrSyntax},
+		// NaNs
+		{"NaN", complex(math.NaN(), 0), nil},
+		{"NANi", complex(0, math.NaN()), nil},
+		{"nan+nAni", complex(math.NaN(), math.NaN()), nil},
+		{"+NaN", 0, ErrSyntax},
+		{"-NaN", 0, ErrSyntax},
+		{"NaN-NaNi", 0, ErrSyntax},
+		// Infs
+		{"Inf", infp0, nil},
+		{"+inf", infp0, nil},
+		{"-inf", infm0, nil},
+		{"Infinity", infp0, nil},
+		{"+INFINITY", infp0, nil},
+		{"-infinity", infm0, nil},
+		{"+infi", inf0p, nil},
+		{"0-infinityi", inf0m, nil},
+		{"Inf+Infi", infpp, nil},
+		{"+Inf-Infi", infpm, nil},
+		{"-Infinity+Infi", infmp, nil},
+		{"inf-inf", 0, ErrSyntax},
+		// Zeros
+		{"0", 0, nil},
+		{"0i", 0, nil},
+		{"-0.0i", 0, nil},
+		{"0+0.0i", 0, nil},
+		{"0e+0i", 0, nil},
+		{"0e-0+0i", 0, nil},
+		{"-0.0-0.0i", 0, nil},
+		{"0e+012345", 0, nil},
+		{"0x0p+012345i", 0, nil},
+		{"0x0.00p-012345i", 0, nil},
+		{"+0e-0+0e-0i", 0, nil},
+		{"0e+0+0e+0i", 0, nil},
+		{"-0e+0-0e+0i", 0, nil},
+		// Regular non-zeroes
+		{"0.1", 0.1, nil},
+		{"0.1i", 0 + 0.1i, nil},
+		{"0.123", 0.123, nil},
+		{"0.123i", 0 + 0.123i, nil},
+		{"0.123+0.123i", 0.123 + 0.123i, nil},
+		{"99", 99, nil},
+		{"+99", 99, nil},
+		{"-99", -99, nil},
+		{"+1i", 1i, nil},
+		{"-1i", -1i, nil},
+		{"+3+1i", 3 + 1i, nil},
+		{"30+3i", 30 + 3i, nil},
+		{"+3e+3-3e+3i", 3e+3 - 3e+3i, nil},
+		{"+3e+3+3e+3i", 3e+3 + 3e+3i, nil},
+		{"+3e+3+3e+3i+", 0, ErrSyntax},
+		// Separators
+		{"0.1", 0.1, nil},
+		{"0.1i", 0 + 0.1i, nil},
+		{"0.1_2_3", 0.123, nil},
+		{"+0x_3p3i", 0x3p3i, nil},
+		{"0x_10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"+0x_1_0.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"0x10.3p+8-0x_3p3i", 0x10.3p+8 - 0x3p3i, nil},
+		// Hexadecimals
+		{"0x10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"+0x10.3p-8+0x3p3i", 0x10.3p-8 + 0x3p3i, nil},
+		{"0x10.3p+8-0x3p3i", 0x10.3p+8 - 0x3p3i, nil},
+		{"0x1p0", 1, nil},
+		{"0x1p1", 2, nil},
+		{"0x1p-1", 0.5, nil},
+		{"0x1ep-1", 15, nil},
+		{"-0x1ep-1", -15, nil},
+		{"-0x2p3", -16, nil},
+		{"0x1e2", 0, ErrSyntax},
+		{"1p2", 0, ErrSyntax},
+		{"0x1e2i", 0, ErrSyntax},
+		// ErrRange
+		// next float64 - too large
+		{"+0x1p1024", infp0, ErrRange},
+		{"-0x1p1024", infm0, ErrRange},
+		{"+0x1p1024i", inf0p, ErrRange},
+		{"-0x1p1024i", inf0m, ErrRange},
+		{"+0x1p1024+0x1p1024i", infpp, ErrRange},
+		{"+0x1p1024-0x1p1024i", infpm, ErrRange},
+		{"-0x1p1024+0x1p1024i", infmp, ErrRange},
+		{"-0x1p1024-0x1p1024i", infmm, ErrRange},
+		// the border is ...158079
+		// borderline - okay
+		{"+0x1.fffffffffffff7fffp1023+0x1.fffffffffffff7fffp1023i", 1.7976931348623157e+308 + 1.7976931348623157e+308i, nil},
+		{"+0x1.fffffffffffff7fffp1023-0x1.fffffffffffff7fffp1023i", 1.7976931348623157e+308 - 1.7976931348623157e+308i, nil},
+		{"-0x1.fffffffffffff7fffp1023+0x1.fffffffffffff7fffp1023i", -1.7976931348623157e+308 + 1.7976931348623157e+308i, nil},
+		{"-0x1.fffffffffffff7fffp1023-0x1.fffffffffffff7fffp1023i", -1.7976931348623157e+308 - 1.7976931348623157e+308i, nil},
+		// borderline - too large
+		{"+0x1.fffffffffffff8p1023", infp0, ErrRange},
+		{"-0x1fffffffffffff.8p+971", infm0, ErrRange},
+		{"+0x1.fffffffffffff8p1023i", inf0p, ErrRange},
+		{"-0x1fffffffffffff.8p+971i", inf0m, ErrRange},
+		{"+0x1.fffffffffffff8p1023+0x1.fffffffffffff8p1023i", infpp, ErrRange},
+		{"+0x1.fffffffffffff8p1023-0x1.fffffffffffff8p1023i", infpm, ErrRange},
+		{"-0x1fffffffffffff.8p+971+0x1fffffffffffff.8p+971i", infmp, ErrRange},
+		{"-0x1fffffffffffff8p+967-0x1fffffffffffff8p+967i", infmm, ErrRange},
+		// a little too large
+		{"1e308+1e308i", 1e+308 + 1e+308i, nil},
+		{"2e308+2e308i", infpp, ErrRange},
+		{"1e309+1e309i", infpp, ErrRange},
+		{"0x1p1025+0x1p1025i", infpp, ErrRange},
+		{"2e308", infp0, ErrRange},
+		{"1e309", infp0, ErrRange},
+		{"0x1p1025", infp0, ErrRange},
+		{"2e308i", inf0p, ErrRange},
+		{"1e309i", inf0p, ErrRange},
+		{"0x1p1025i", inf0p, ErrRange},
+		// way too large
+		{"+1e310+1e310i", infpp, ErrRange},
+		{"+1e310-1e310i", infpm, ErrRange},
+		{"-1e310+1e310i", infmp, ErrRange},
+		{"-1e310-1e310i", infmm, ErrRange},
+		// under/overflow exponent
+		{"1e-4294967296", 0, nil},
+		{"1e-4294967296i", 0, nil},
+		{"1e-4294967296+1i", 1i, nil},
+		{"1+1e-4294967296i", 1, nil},
+		{"1e-4294967296+1e-4294967296i", 0, nil},
+		{"1e+4294967296", infp0, ErrRange},
+		{"1e+4294967296i", inf0p, ErrRange},
+		{"1e+4294967296+1e+4294967296i", infpp, ErrRange},
+		{"1e+4294967296-1e+4294967296i", infpm, ErrRange},
+	}
+	for _, tt := range tests {
+		tt := tt // for capture in Run closures below
+		if tt.err != nil {
+			tt.err = &NumError{Func: "ParseComplex", Num: tt.in, Err: tt.err}
+		}
+		t.Run(tt.in, func(t *testing.T) {
+			got, err := ParseComplex(tt.in, 128)
+			if !reflect.DeepEqual(err, tt.err) {
+				t.Fatalf("ParseComplex(%q, 128) = %v, %v want %v, %v", tt.in, got, err, tt.out, tt.err)
+			}
+			if !(cmplx.IsNaN(tt.out) && cmplx.IsNaN(got)) && got != tt.out {
+				t.Fatalf("ParseComplex(%q, 128) = %v, %v want %v, %v", tt.in, got, err, tt.out, tt.err)
+			}
+		})
+	}
+}
diff --git a/src/strconv/atof.go b/src/strconv/atof.go
index 28ad0940801967..f20ae4af09b44f 100644
--- a/src/strconv/atof.go
+++ b/src/strconv/atof.go
@@ -677,8 +677,8 @@ func atof64(s string) (f float64, n int, err error) {
 // away from the largest floating point number of the given size,
 // ParseFloat returns f = ±Inf, err.Err = ErrRange.
 //
-// ParseFloat recognizes the strings "NaN", "+Inf", and "-Inf" as their
-// respective special floating point values. It ignores case when matching.
+// ParseFloat recognizes the strings "NaN", and the (possibly signed) strings "Inf" and "Infinity"
+// as their respective special floating point values. It ignores case when matching.
 func ParseFloat(s string, bitSize int) (float64, error) {
 	f, n, err := parseFloatPrefix(s, bitSize)
 	if err == nil && n != len(s) {
diff --git a/src/strconv/atoi.go b/src/strconv/atoi.go
index 0b82fb09085cb0..f6c4efaef60165 100644
--- a/src/strconv/atoi.go
+++ b/src/strconv/atoi.go
@@ -22,7 +22,7 @@ var ErrSyntax = errors.New("invalid syntax")
 
 // A NumError records a failed conversion.
 type NumError struct {
-	Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat)
+	Func string // the failing function (ParseBool, ParseInt, ParseUint, ParseFloat, ParseComplex)
 	Num  string // the input
 	Err  error  // the reason the conversion failed (e.g. ErrRange, ErrSyntax, etc.)
 }
diff --git a/src/strconv/ctoa.go b/src/strconv/ctoa.go
new file mode 100644
index 00000000000000..c16a2e579cf147
--- /dev/null
+++ b/src/strconv/ctoa.go
@@ -0,0 +1,27 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package strconv
+
+// FormatComplex converts the complex number c to a string of the
+// form (a+bi) where a and b are the real and imaginary parts,
+// formatted according to the format fmt and precision prec.
+//
+// The format fmt and precision prec have the same meaning as in FormatFloat.
+// It rounds the result assuming that the original was obtained from a complex
+// value of bitSize bits, which must be 64 for complex64 and 128 for complex128.
+func FormatComplex(c complex128, fmt byte, prec, bitSize int) string {
+	if bitSize != 64 && bitSize != 128 {
+		panic("invalid bitSize")
+	}
+	bitSize >>= 1 // complex64 uses float32 internally
+
+	// Check if imaginary part has a sign. If not, add one.
+	im := FormatFloat(imag(c), fmt, prec, bitSize)
+	if im[0] != '+' && im[0] != '-' {
+		im = "+" + im
+	}
+
+	return "(" + FormatFloat(real(c), fmt, prec, bitSize) + im + "i)"
+}