diff --git a/bin/nyc.js b/bin/nyc.js
index d28d6e510..d7c070a81 100755
--- a/bin/nyc.js
+++ b/bin/nyc.js
@@ -23,12 +23,10 @@ const config = configUtil.loadConfig(yargs.parse(instrumenterArgs))
 configUtil.addCommandsAndHelp(yargs)
 const argv = yargs.config(config).parse(instrumenterArgs)
 
-if (argv._[0] === 'report') {
-  // look in lib/commands/report.js for logic.
-} else if (argv._[0] === 'check-coverage') {
-  // look in lib/commands/check-coverage.js for logic.
-} else if (argv._[0] === 'instrument') {
-  // look in lib/commands/instrument.js for logic.
+if ([
+  'check-coverage', 'report', 'instrument', 'merge'
+].indexOf(argv._[0]) !== -1) {
+  // look in lib/commands for logic.
 } else if (argv._.length) {
   // if instrument is set to false,
   // enable a noop instrumenter.
diff --git a/index.js b/index.js
index 3bf3fdaeb..dd1428a82 100755
--- a/index.js
+++ b/index.js
@@ -421,13 +421,13 @@ function coverageFinder () {
   return coverage
 }
 
-NYC.prototype._getCoverageMapFromAllCoverageFiles = function () {
+NYC.prototype.getCoverageMapFromAllCoverageFiles = function (baseDirectory) {
   var _this = this
   var map = libCoverage.createCoverageMap({})
 
-  this.eachReport(function (report) {
+  this.eachReport(undefined, (report) => {
     map.merge(report)
-  })
+  }, baseDirectory)
   // depending on whether source-code is pre-instrumented
   // or instrumented using a JIT plugin like babel-require
   // you may opt to exclude files after applying
@@ -443,7 +443,7 @@ NYC.prototype._getCoverageMapFromAllCoverageFiles = function () {
 
 NYC.prototype.report = function () {
   var tree
-  var map = this._getCoverageMapFromAllCoverageFiles()
+  var map = this.getCoverageMapFromAllCoverageFiles()
   var context = libReport.createContext({
     dir: this.reportDirectory(),
     watermarks: this.config.watermarks
@@ -469,7 +469,7 @@ NYC.prototype.showProcessTree = function () {
 }
 
 NYC.prototype.checkCoverage = function (thresholds, perFile) {
-  var map = this._getCoverageMapFromAllCoverageFiles()
+  var map = this.getCoverageMapFromAllCoverageFiles()
   var nyc = this
 
   if (perFile) {
@@ -516,20 +516,22 @@ NYC.prototype._loadProcessInfos = function () {
   })
 }
 
-NYC.prototype.eachReport = function (filenames, iterator) {
+NYC.prototype.eachReport = function (filenames, iterator, baseDirectory) {
+  baseDirectory = baseDirectory || this.tempDirectory()
+
   if (typeof filenames === 'function') {
     iterator = filenames
     filenames = undefined
   }
 
   var _this = this
-  var files = filenames || fs.readdirSync(this.tempDirectory())
+  var files = filenames || fs.readdirSync(baseDirectory)
 
   files.forEach(function (f) {
     var report
     try {
       report = JSON.parse(fs.readFileSync(
-        path.resolve(_this.tempDirectory(), f),
+        path.resolve(baseDirectory, f),
         'utf-8'
       ))
 
@@ -545,7 +547,7 @@ NYC.prototype.eachReport = function (filenames, iterator) {
 NYC.prototype.loadReports = function (filenames) {
   var reports = []
 
-  this.eachReport(filenames, function (report) {
+  this.eachReport(filenames, (report) => {
     reports.push(report)
   })
 
diff --git a/lib/commands/merge.js b/lib/commands/merge.js
new file mode 100644
index 000000000..f660092d1
--- /dev/null
+++ b/lib/commands/merge.js
@@ -0,0 +1,51 @@
+'use strict'
+const fs = require('fs')
+
+var NYC
+try {
+  NYC = require('../../index.covered.js')
+} catch (e) {
+  NYC = require('../../index.js')
+}
+
+exports.command = 'merge <input-directory> [output-file]'
+
+exports.describe = 'merge istanbul format coverage output in a given folder'
+
+exports.builder = function (yargs) {
+  return yargs
+    .positional('input-directory', {
+      describe: 'directory containing multiple istanbul coverage files',
+      type: 'text',
+      default: './.nyc_output'
+    })
+    .positional('output-file', {
+      describe: 'file to output combined istanbul format coverage to',
+      type: 'text',
+      default: 'coverage.json'
+    })
+    .option('temp-directory', {
+      describe: 'directory to read raw coverage information from',
+      default: './.nyc_output'
+    })
+    .example('$0 merge ./out coverage.json', 'merge together reports in ./out and output as coverage.json')
+}
+
+exports.handler = function (argv) {
+  process.env.NYC_CWD = process.cwd()
+  const nyc = new NYC(argv)
+  let inputStat
+  try {
+    inputStat = fs.statSync(argv.inputDirectory)
+    if (!inputStat.isDirectory()) {
+      console.error(`${argv.inputDirectory} was not a directory`)
+      process.exit(1)
+    }
+  } catch (err) {
+    console.error(`failed access input directory ${argv.inputDirectory} with error:\n\n${err.message}`)
+    process.exit(1)
+  }
+  const map = nyc.getCoverageMapFromAllCoverageFiles(argv.inputDirectory)
+  fs.writeFileSync(argv.outputFile, JSON.stringify(map, null, 2), 'utf8')
+  console.info(`coverage files in ${argv.inputDirectory} merged into ${argv.outputFile}`)
+}
diff --git a/lib/config-util.js b/lib/config-util.js
index 170e1d701..b202ab445 100644
--- a/lib/config-util.js
+++ b/lib/config-util.js
@@ -243,6 +243,7 @@ Config.addCommandsAndHelp = function (yargs) {
     .command(require('../lib/commands/check-coverage'))
     .command(require('../lib/commands/instrument'))
     .command(require('../lib/commands/report'))
+    .command(require('../lib/commands/merge'))
 }
 
 module.exports = Config
diff --git a/lib/process-args.js b/lib/process-args.js
index df6bcaac1..695f8e62a 100644
--- a/lib/process-args.js
+++ b/lib/process-args.js
@@ -2,7 +2,8 @@ const parser = require('yargs-parser')
 const commands = [
   'report',
   'check-coverage',
-  'instrument'
+  'instrument',
+  'merge'
 ]
 
 module.exports = {
diff --git a/test/fixtures/cli/merge-input/a.json b/test/fixtures/cli/merge-input/a.json
new file mode 100644
index 000000000..81f0ba143
--- /dev/null
+++ b/test/fixtures/cli/merge-input/a.json
@@ -0,0 +1,200 @@
+{
+  "/private/tmp/contrived/library.js": {
+    "path": "/private/tmp/contrived/library.js",
+    "statementMap": {
+      "0": {
+        "start": {
+          "line": 1,
+          "column": 0
+        },
+        "end": {
+          "line": 15,
+          "column": 1
+        }
+      },
+      "1": {
+        "start": {
+          "line": 3,
+          "column": 4
+        },
+        "end": {
+          "line": 3,
+          "column": 16
+        }
+      },
+      "2": {
+        "start": {
+          "line": 6,
+          "column": 4
+        },
+        "end": {
+          "line": 6,
+          "column": 16
+        }
+      },
+      "3": {
+        "start": {
+          "line": 9,
+          "column": 4
+        },
+        "end": {
+          "line": 13,
+          "column": 5
+        }
+      },
+      "4": {
+        "start": {
+          "line": 10,
+          "column": 6
+        },
+        "end": {
+          "line": 10,
+          "column": 14
+        }
+      },
+      "5": {
+        "start": {
+          "line": 12,
+          "column": 6
+        },
+        "end": {
+          "line": 12,
+          "column": 14
+        }
+      }
+    },
+    "fnMap": {
+      "0": {
+        "name": "(anonymous_0)",
+        "decl": {
+          "start": {
+            "line": 2,
+            "column": 11
+          },
+          "end": {
+            "line": 2,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 2,
+            "column": 21
+          },
+          "end": {
+            "line": 4,
+            "column": 3
+          }
+        },
+        "line": 2
+      },
+      "1": {
+        "name": "(anonymous_1)",
+        "decl": {
+          "start": {
+            "line": 5,
+            "column": 11
+          },
+          "end": {
+            "line": 5,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 5,
+            "column": 21
+          },
+          "end": {
+            "line": 7,
+            "column": 3
+          }
+        },
+        "line": 5
+      },
+      "2": {
+        "name": "(anonymous_2)",
+        "decl": {
+          "start": {
+            "line": 8,
+            "column": 11
+          },
+          "end": {
+            "line": 8,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 8,
+            "column": 18
+          },
+          "end": {
+            "line": 14,
+            "column": 3
+          }
+        },
+        "line": 8
+      }
+    },
+    "branchMap": {
+      "0": {
+        "loc": {
+          "start": {
+            "line": 9,
+            "column": 4
+          },
+          "end": {
+            "line": 13,
+            "column": 5
+          }
+        },
+        "type": "if",
+        "locations": [
+          {
+            "start": {
+              "line": 9,
+              "column": 4
+            },
+            "end": {
+              "line": 13,
+              "column": 5
+            }
+          },
+          {
+            "start": {
+              "line": 9,
+              "column": 4
+            },
+            "end": {
+              "line": 13,
+              "column": 5
+            }
+          }
+        ],
+        "line": 9
+      }
+    },
+    "s": {
+      "0": 1,
+      "1": 1,
+      "2": 0,
+      "3": 1,
+      "4": 0,
+      "5": 1
+    },
+    "f": {
+      "0": 1,
+      "1": 0,
+      "2": 1
+    },
+    "b": {
+      "0": [
+        0,
+        1
+      ]
+    },
+    "_coverageSchema": "332fd63041d2c1bcb487cc26dd0d5f7d97098a6c",
+    "hash": "e86c0c0fa7c4fadac81e2479bfba3c0d59b657aa"
+  }
+}
\ No newline at end of file
diff --git a/test/fixtures/cli/merge-input/b.json b/test/fixtures/cli/merge-input/b.json
new file mode 100644
index 000000000..bbef81594
--- /dev/null
+++ b/test/fixtures/cli/merge-input/b.json
@@ -0,0 +1,200 @@
+{
+  "/private/tmp/contrived/library.js": {
+    "path": "/private/tmp/contrived/library.js",
+    "statementMap": {
+      "0": {
+        "start": {
+          "line": 1,
+          "column": 0
+        },
+        "end": {
+          "line": 15,
+          "column": 1
+        }
+      },
+      "1": {
+        "start": {
+          "line": 3,
+          "column": 4
+        },
+        "end": {
+          "line": 3,
+          "column": 16
+        }
+      },
+      "2": {
+        "start": {
+          "line": 6,
+          "column": 4
+        },
+        "end": {
+          "line": 6,
+          "column": 16
+        }
+      },
+      "3": {
+        "start": {
+          "line": 9,
+          "column": 4
+        },
+        "end": {
+          "line": 13,
+          "column": 5
+        }
+      },
+      "4": {
+        "start": {
+          "line": 10,
+          "column": 6
+        },
+        "end": {
+          "line": 10,
+          "column": 14
+        }
+      },
+      "5": {
+        "start": {
+          "line": 12,
+          "column": 6
+        },
+        "end": {
+          "line": 12,
+          "column": 14
+        }
+      }
+    },
+    "fnMap": {
+      "0": {
+        "name": "(anonymous_0)",
+        "decl": {
+          "start": {
+            "line": 2,
+            "column": 11
+          },
+          "end": {
+            "line": 2,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 2,
+            "column": 21
+          },
+          "end": {
+            "line": 4,
+            "column": 3
+          }
+        },
+        "line": 2
+      },
+      "1": {
+        "name": "(anonymous_1)",
+        "decl": {
+          "start": {
+            "line": 5,
+            "column": 11
+          },
+          "end": {
+            "line": 5,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 5,
+            "column": 21
+          },
+          "end": {
+            "line": 7,
+            "column": 3
+          }
+        },
+        "line": 5
+      },
+      "2": {
+        "name": "(anonymous_2)",
+        "decl": {
+          "start": {
+            "line": 8,
+            "column": 11
+          },
+          "end": {
+            "line": 8,
+            "column": 12
+          }
+        },
+        "loc": {
+          "start": {
+            "line": 8,
+            "column": 18
+          },
+          "end": {
+            "line": 14,
+            "column": 3
+          }
+        },
+        "line": 8
+      }
+    },
+    "branchMap": {
+      "0": {
+        "loc": {
+          "start": {
+            "line": 9,
+            "column": 4
+          },
+          "end": {
+            "line": 13,
+            "column": 5
+          }
+        },
+        "type": "if",
+        "locations": [
+          {
+            "start": {
+              "line": 9,
+              "column": 4
+            },
+            "end": {
+              "line": 13,
+              "column": 5
+            }
+          },
+          {
+            "start": {
+              "line": 9,
+              "column": 4
+            },
+            "end": {
+              "line": 13,
+              "column": 5
+            }
+          }
+        ],
+        "line": 9
+      }
+    },
+    "s": {
+      "0": 1,
+      "1": 0,
+      "2": 1,
+      "3": 1,
+      "4": 1,
+      "5": 0
+    },
+    "f": {
+      "0": 0,
+      "1": 1,
+      "2": 1
+    },
+    "b": {
+      "0": [
+        1,
+        0
+      ]
+    },
+    "_coverageSchema": "332fd63041d2c1bcb487cc26dd0d5f7d97098a6c",
+    "hash": "e86c0c0fa7c4fadac81e2479bfba3c0d59b657aa"
+  }
+}
\ No newline at end of file
diff --git a/test/nyc-bin.js b/test/nyc-bin.js
index fb7752328..5a2cb937f 100644
--- a/test/nyc-bin.js
+++ b/test/nyc-bin.js
@@ -972,6 +972,81 @@ describe('the nyc cli', function () {
       })
     })
   })
+
+  describe('merge', () => {
+    it('combines multiple coverage reports', (done) => {
+      const args = [
+        bin,
+        'merge',
+        './merge-input'
+      ]
+
+      const proc = spawn(process.execPath, args, {
+        cwd: fixturesCLI,
+        env: env
+      })
+
+      proc.on('close', function (code) {
+        const mergedCoverage = require('./fixtures/cli/coverage')
+        // the combined reports should have 100% function
+        // branch and statement coverage.
+        mergedCoverage['/private/tmp/contrived/library.js']
+          .s.should.eql({'0': 2, '1': 1, '2': 1, '3': 2, '4': 1, '5': 1})
+        mergedCoverage['/private/tmp/contrived/library.js']
+          .f.should.eql({'0': 1, '1': 1, '2': 2})
+        mergedCoverage['/private/tmp/contrived/library.js']
+          .b.should.eql({'0': [1, 1]})
+        rimraf.sync(path.resolve(fixturesCLI, 'coverage.json'))
+        return done()
+      })
+    })
+
+    it('reports error if input directory is missing', (done) => {
+      const args = [
+        bin,
+        'merge',
+        './DIRECTORY_THAT_IS_MISSING'
+      ]
+
+      const proc = spawn(process.execPath, args, {
+        cwd: fixturesCLI,
+        env: env
+      })
+
+      var stderr = ''
+      proc.stderr.on('data', function (chunk) {
+        stderr += chunk
+      })
+
+      proc.on('close', function (code) {
+        stderr.should.match(/failed access input directory/)
+        return done()
+      })
+    })
+
+    it('reports error if input is not a directory', (done) => {
+      const args = [
+        bin,
+        'merge',
+        './package.json'
+      ]
+
+      const proc = spawn(process.execPath, args, {
+        cwd: fixturesCLI,
+        env: env
+      })
+
+      var stderr = ''
+      proc.stderr.on('data', function (chunk) {
+        stderr += chunk
+      })
+
+      proc.on('close', function (code) {
+        stderr.should.match(/was not a directory/)
+        return done()
+      })
+    })
+  })
 })
 
 function stdoutShouldEqual (stdout, expected) {